What does this validator actually check?

It checks three things. First, whether the leading prefix (e.g. 07, 020, 0800) is allocated in the Ofcom National Telephone Numbering Plan. Second, whether the total digit count matches the expected length for that range (almost always 11 digits in national format, or 10 for a small number of legacy codes). Third, it identifies the service class so you know at a glance whether it is a mobile, landline, freephone, revenue-sharing or premium-rate number. It does not make a live network query, so it cannot confirm whether the number is currently active or assigned to a subscriber.

What is E.164 format and why does it matter?

E.164 is the ITU international numbering format used by databases, APIs, SMS gateways and VoIP platforms. A UK number in E.164 looks like +447700900123 — no leading zero, country code prefix +44, no spaces. Using E.164 eliminates ambiguity when storing or transmitting numbers across systems that may not know the local dialling convention.

Can I enter the number with spaces, dashes or brackets?

Yes. The validator strips spaces, dashes, dots and parentheses before checking, so 07700 900-123, (0161) 234 5678 and 07700900123 are all treated identically. You can also use the international prefix +44 or 0044 in place of the leading 0.

Why does a number show as invalid even though I dialled it successfully?

A structurally valid number (correct prefix and length) will show as valid here. If a number passes this check but is not connecting, the issue is at the network or subscription level — the number may be unallocated, ported, suspended or simply out of service. This tool checks format only, not live network status.

What is the difference between 01/02 geographic and 03 non-geographic numbers?

Numbers starting 01 or 02 are geographic — they are tied to a specific UK city or region and the area code tells you where the exchange is (e.g. 0161 is Manchester, 020 is London). Numbers starting 03 are non-geographic — they can be used anywhere in the UK and must be charged at the same rate as a geographic call, making them popular for charities, government services and businesses that want a single national number without premium-rate costs.

Are 0800 and 0808 numbers really free from mobiles?

Since July 2015, yes. Ofcom rules require all UK mobile operators to allow free calls to 0800 and 0808 numbers. Before that date, many mobile contracts charged for freephone calls, which is why the old advice to use 03 alternatives persisted for a while. Both 0800 and 0808 are now genuinely free from any UK mobile or landline.

UK Phone Number Validator

UK phone numbers follow a strict national numbering plan maintained by Ofcom, the UK’s communications regulator. Each number range has a designated service class, a fixed digit length and specific rules about how it may be used and charged. This validator checks any UK phone number against that plan entirely in your browser — no number you enter is ever sent to a server.

How the validation works

The tool implements the Ofcom National Telephone Numbering Plan (last updated 2024). When you enter a number, it goes through four stages.

Stage 1 — Normalisation. Spaces, dashes, dots and parentheses are removed. International prefixes (+44 or 0044) are converted to a national leading zero so that +44 7700 900123 and 07700 900123 are treated as the same input.

Stage 2 — Character and length checks. The normalised string must contain only digits and start with 0. The total digit count must be between 10 and 11 (a small legacy range, 0500 freephone, uses 10; almost all current numbers use 11).

Stage 3 — Prefix matching. The number’s leading digits are matched against the Ofcom allocation table, searching from the longest prefix to the shortest to find the most specific rule. Each entry in the table carries a service class (Mobile, Geographic, Non-geographic, Freephone, Revenue-sharing, Premium), the expected total digit count and a flag for whether the range is dialable from UK mobiles without extra charges.

Stage 4 — Result. If the prefix is allocated and the length matches, the number is valid. The tool then formats it in the standard national style (e.g. 07xxx xxxxxx for mobiles, 01xxx xxxxxx for geographic) and in E.164 format (+44…) for copying.

Number range quick reference

Prefix	Service	Mobile dialable
07	Mobile	Yes
020, 023, 024, 028, 029	Geographic (city codes)	Yes
01	Geographic (area codes)	Yes
03	Non-geographic, local rate	Yes
0800, 0808	Freephone	Yes (free since 2015)
0843–0845	Revenue-sharing	Yes (extra charge may apply)
0870–0873	Revenue-sharing	Yes (extra charge may apply)
09	Premium rate	Often restricted

Worked example

Suppose you receive the number +44 (0)20 7946 0958 on a form submission.

After normalisation: 02079460958 — 11 digits, starts with 020.
The prefix 020 matches the London geographic range; expected length is 11 digits.
Length check: 11 = 11. Pass.
Formatted national output: 020 7946 0958. E.164 output: +442079460958.

The number range 020 7946 is actually Ofcom’s reserved drama/roleplay range, so it is structurally valid but never belongs to a real subscriber — useful for testing.

A second example: 0845 123 4567. This normalises to 08451234567, matches the 0845 lo-call revenue-sharing range, has the correct length of 11 digits, and is therefore structurally valid. However it carries a note that extra charges may apply from mobiles, which the validator surfaces in the result.

All processing happens locally. Your number never leaves the page.