Who Called Me from 01245 (Chelmsford)?

01245 is the UK dialling code for Chelmsford, in the historic county of Essex, covering an area with a population of approximately 168,310. Numbers in this area follow the format 012451234567 — the dialling code, followed by a local number assigned to a specific Communications Provider (CP).

Ofcom has allocated 247 number blocks within the 01245 range, spread across BT, Virgin Media, Sky, TalkTalk, Gamma and many smaller UK CPs. Each block of 1,000 (or sometimes 10,000) numbers is owned by a single CP, which may then assign individual numbers to its own customers or to resellers further down the chain. You can see the full block-by-block allocation list below.

Although 01245 originally indicated the geographic location of the line, UK number portability means a phone with this prefix can technically be located anywhere. For most landlines the geographic match still holds, but for VoIP-only numbers it does not. If you receive a call from a 01245 number and you don't recognise it, you can match the next four digits (the "block") against the table below to identify the originally-allocated network operator.