0203 London (020 3) numbers UK

About 0203 numbers in the UK

The 0203 prefix is part of the UK National Telephone Numbering Plan administered by Ofcom and falls into the Geographic family. 0203 is not a separate area code — it is London's 020 code followed by local numbers beginning 3, released in 2005 when the original 020 7 and 020 8 stock ran low. Calls cost the same as any UK landline.

Ofcom allocates 0203 number ranges to UK communications providers (Range Holders) in 1,000- or 10,000-number blocks. The table below lists every currently-allocated block we have ingested from Ofcom’s weekly Numbering Data feed. Click any Range Holder to see their full UK portfolio, or paste a specific number into the lookup form above to see the originating provider, the allocation status, and a live AI internet check for any public reports about that exact number.

For a deeper explainer on how UK number prefixes are organised, see UK area codes explained, How Ofcom allocates UK phone numbers, and the UK phone number format guide. If you have received a 0203 call you are unsure about, our who-called-me UK guide walks through the safe identification routine in under a minute.

0203 ranges currently in the Ofcom data

Our most recent Ofcom snapshot lists 200 individual number ranges currently allocated on the 0203 prefix, spread across 33 Ofcom-listed Range Holders. The top 5 holders by allocated block count are BT (50), Colt Technology Services (20), Gamma Telecom Holdings Limited (16), Verizon UK Limited (10) and Vodafone Ltd (C&W) (8). The dominant allocation status across 0203 blocks is Allocated (87% of the visible ranges), followed by Protected at 13%.

Spotting a fake 0203 call

• Check the Range Holder column below: a 0203 number that doesn’t map cleanly to one of the UK-licensed providers listed is the first amber flag. Genuine UK callers on this prefix come through one of the carriers Ofcom has actually allocated the block to.
• Watch the script. Legitimate 0203 callers — whether banks, delivery firms, public-sector services or commercial brands — don’t pressure you into reading codes from a text, keying in passwords, or installing remote-access software while still on the line.
• If you weren’t expecting a 0203 call, hang up and ring back via a number printed on the organisation’s website or a recent letter, not the CLI that just rang you. Most 0203 scams collapse the moment you switch to a verified channel.
• Paste the exact digits into the lookup form above for a live AI internet check. If the number has been mass-reported on consumer forums, that surfaces in the per-number result alongside the structured Ofcom Range Holder data.