8-14

characters

Typical MSN length

F / 14P / 15P

electricity SMETS2

Should keep working on switch

G4P

gas SMETS2

Should keep working on switch

Why most MSN guides miss the point

Search "what is a meter serial number" and you will find a hundred pages telling you the MSN is an 8 to 14 character code near the barcode, used by suppliers for admin. That is true and useless. The MSN is the only field on your bill that encodes the generation of your smart meter, and meter generation is what decides whether your in-home display keeps showing live usage when a new supplier takes over.

By the end of Q4 2025, 71% of UK domestic meters were classed as smart in the GOV.UK rollout statistics, but a large minority are SMETS1, the pre-2018 first generation. SMETS1 meters were not built to be supplier-agnostic. Ofgem and the DCC ran a multi-year migration to bring them under the same central network as SMETS2, but the migration is imperfect: many SMETS1 meters still drop into "dumb mode" on the day of a switch. Customers blame the new supplier ; the real cause is on the meter face. The MSN tells you, before you switch, which side of the line you sit on.

The one-line rule. If your electricity MSN starts with F, 14P or 15P, or your gas MSN starts with G4P, you have a SMETS2 device and your smart functionality should survive a supplier switch. Any other prefix is worth investigating before you commit.

What an MSN looks like and where to find it

A Meter Serial Number is a short alphanumeric string, typically 8 to 14 characters long, stamped or printed on the front of every electricity and gas meter installed in Great Britain. It sits near the barcode on modern meters, or beside the dials on older mechanical ones. The label rarely says "MSN" outright ; you recognise it by shape and position.

A worked example for a SMETS2 electricity meter: 14P0021987654. The 14P prefix identifies the generation, the rest is a manufacturer-issued unique number. A SMETS2 gas meter looks like G4P11209876543.

You can also find the MSN on any recent bill, paper or PDF, in the "Meter readings" block. Different suppliers label it "Meter Number", "Serial No.", "Meter ID" or "MSN" ; there is no industry standard. On a dual-fuel bill the electricity MSN appears in the electricity block and the gas MSN in the gas block, even from the same supplier.

If you share a meter cupboard with neighbours, always cross-check the MSN on your bill against the device on the wall. Mislabelled meters in shared cupboards are a common cause of being billed for a neighbour's consumption.

MSN prefixes and what they tell you

The first 2 to 4 characters of the MSN are the diagnostic. They encode the fuel, the generation, and sometimes the manufacturer.

SMETS1 electricity prefixes (the legacy generation)

SMETS1 was the first generation of UK smart meters, rolled out 2013 to 2018. Common SMETS1 electricity prefixes you may still see are K, S and certain numeric codes used by Secure, Itron and Landis+Gyr batches . These meters were tied to the installing supplier's bespoke head-end system. They have since been migrated onto the DCC central network in waves, but the migration is not universal: meters with old firmware or whose original supplier exited the market in 2021 to 2022 may still drop into dumb mode on a switch. The prefix is your earliest warning.

SMETS2 electricity prefixes (F, 14P, 15P)

SMETS2 has been the mandated standard for new installations since 2018. SMETS2 electricity meters communicate directly with the DCC central network from day one, regardless of supplier. The prefixes you will see are:

  • F followed by digits: typically Aclara and EDMI SMETS2 electricity meters ;
  • 14P: an older SMETS2 production batch, widely deployed during the 2019 to 2021 ramp-up;
  • 15P: a newer SMETS2 production batch, deployed from late 2021 onwards.

All three should survive a supplier switch without losing smart functionality. The DCC's planned VWAN service launch in 2026 further hardens the SMETS2 estate against connectivity gaps in areas where the original Telefonica WAN was patchy.

SMETS2 gas prefixes (G4P)

SMETS2 gas meters use the G4P prefix universally. The gas meter is a battery-powered slave to the electricity meter's communications hub, so a G4P gas meter only behaves as a smart meter when the paired electricity meter is also SMETS2. If you have a SMETS1 electricity meter and a G4P gas meter, gas readings may stop after a switch until the hub re-pairs.

Older mechanical and miscellaneous prefixes

Fully mechanical electricity meters use a short numeric or single-letter MSN with no recognisable smart prefix. Traditional gas meters often start with L and end in M. These devices are not smart and never will be ; switching is straightforward precisely because there is nothing intelligent to break.

The MSN is your switch-time diagnostic

Here is the insider truth no comparison site puts on its switching page: SMETS1 meters frequently fall into dumb mode after a supplier switch, even after the DCC migration. The in-home display goes blank, automatic readings stop, and the new supplier reverts to estimated bills. The customer blames the new supplier ; the supplier blames "industry processes". The real cause is meter generation, encoded in the MSN, never properly migrated to the central network.

You can detect the risk before you switch. Read the prefix off your meter or bill, match it against the prefixes above, and use the lookup widget further down. If you have a SMETS1 prefix and you intend to switch, here is the script to use with your prospective new supplier on day one:

  1. Confirm whether they can read your specific SMETS1 meter on the DCC migrated estate;
  2. Ask them to commit, in writing, to a SMETS2 upgrade visit within 90 days if smart functionality is lost;
  3. Request that you stay on submitted manual readings (not estimates) until the upgrade is complete;
  4. Note your current MSN before the switch, so you can prove which device was installed at the supply point on the day you signed up.

The same script protects you if your electricity meter is SMETS2 but your gas meter is older than G4P. Most suppliers will replace a mismatched pair as routine cleanup, but only if you ask.

SMETS1 dumb mode insider note. If your smart functionality stops after a switch and your MSN prefix is K, S or another SMETS1 marker, this is not a fault with your new supplier. Open a complaint citing the SMETS1 migration gap and request a SMETS2 replacement under the supplier's smart rollout obligation. You should not have to pay for the visit.

MSN vs MPAN vs MPRN: three numbers people confuse

The MSN is one of three identifiers that appear on a UK energy bill. They are not interchangeable, and confusing them is one of the most common reasons a switch stalls or a billing dispute drags on for months.

Comparison of MSN, MPAN and MPRN identifiers on UK energy bills
Identifier What it identifies Changes when Typical format
MSN The physical meter on your wall The meter is physically swapped 8 to 14 chars, e.g. 14P0021987654
MPAN The electricity supply point at the address Never (tied to the property) 21 digits, "S" + grid layout
MPRN The gas supply point at the address Never (tied to the property) 6 to 10 digits

In short: MPAN and MPRN are about the address ; the MSN is about the device. Replace the meter and the MSN changes ; the MPAN and MPRN do not. Move home and all three change.

When you'll be asked for your MSN

You will be asked for the MSN whenever a supplier or engineer needs to identify the exact physical meter at your property, rather than the supply point it serves:

  1. Switching supplier: the MSN is the fallback identifier when the MPAN or MPRN is not to hand, and it is what the new supplier checks to confirm your smart meter generation;
  2. Reporting a fault: if your IHD goes blank, readings stop or the meter beeps, the engineer needs the MSN to locate the device on the DCC inventory;
  3. Requesting a SMETS2 upgrade: the MSN is the only way the supplier can confirm what is currently installed. With Ofgem setting the typical dual-fuel Direct Debit cap at £1,862 per year from 1 July 2026 (up from £1,641 in the April to June period), accurate metering matters more than ever;
  4. Moving home: on move-in day, note every MSN and opening reading you find. The MSN is your evidence if a later bill quotes a meter that was not in the property when you arrived.

Look up your meter from its serial number

Type the first 2 to 4 characters of your MSN below. The lookup tells you the likely meter generation, fuel and whether your smart functionality should survive a supplier switch.

Try an example:

Switching outlook:

Start typing your MSN to see what it means.

Indicative only. Some manufacturers share prefixes ; if your meter is borderline, your supplier can confirm the generation from the DCC inventory.

Frequently asked questions

No. The MSN identifies the physical meter, while the MPAN (electricity) and MPRN (gas) identify the supply point at your address. The MSN changes when the meter is swapped; the MPAN and MPRN stay the same for the lifetime of the property.

Read the prefix off the MSN. SMETS2 prefixes (F, 14P, 15P for electricity and G4P for gas) survive a switch in the vast majority of cases. SMETS1 prefixes (commonly K or S on electricity) frequently fall into dumb mode after a switch, even though the DCC migration was supposed to fix this. If you have a SMETS1 prefix, request a SMETS2 upgrade visit from the new supplier on day one.

No. Switching is an administrative change at the supply point level. The physical meter stays in place, so the MSN does not change. Only a hardware replacement produces a new MSN.

Between 8 and 14 alphanumeric characters. Gas MSNs tend to be longer than electricity MSNs. The exact length depends on the manufacturer and the SMETS generation.

On an electricity smart meter the MSN is next to the barcode on the front face and commonly starts with F, 14P or 15P. On a gas smart meter it is next to the barcode and starts with G4P. The in-home display (IHD) does not show the MSN.

Contact your supplier with photographs of both the meter face and the bill. A mismatch usually means the account is linked to a neighbour's device, especially in shared meter cupboards. If the supplier cannot resolve the dispute within eight weeks, you can escalate to the Energy Ombudsman free of charge.

Next steps

Once you know which side of the SMETS1/SMETS2 line you sit on, keep your MSN alongside your MPAN and MPRN. You will need all three the next time you switch, move home or submit a meter reading.