UK Phone Number Format: +44, the Dropped Zero, and Prefixes Explained

A UK phone number is written with a leading 0 at home and with +44 instead of the 0 internationally. 07400 123456 becomes +44 7400 123456; 020 7946 0958 becomes +44 20 7946 0958. In E.164 (no spaces) that's +447400123456 and +442079460958. Most UK numbers are 11 digits with the 0, or 10 after +44.

The single most common conversion mistake is keeping the zero: +4402079460958 is wrong.

What the prefixes mean

Starts with	Type	Example (national format)
01, 02	Geographic landline	020 7946 0958 (London), 0161 496 0000 (Manchester)
03	Non-geographic, charged like a landline	0303 123 4567
071–075, 077–079	Mobile	07400 123456
070	Personal number (forwards to another phone)	070 1234 5678
076	Mostly pagers
0800, 0808	Freephone	0800 123 4567
084, 087	Service numbers, extra charge	0845 123 4567
09	Premium rate	09001 234567

So the prefix tells you the line type, which is much more than US numbers tell you (see US phone number format). A list of UK leads can be sorted into mobiles, landlines and switchboards with a free check.

070 is the trap: it looks like a mobile but is a forwarding service, and 070 numbers have a history of being used in scams. libphonenumber labels them PERSONAL_NUMBER, not mobile.

Converting UK numbers to E.164

1. Remove spaces, brackets and dashes.
2. If it starts with 0, drop the 0 and add +44.
3. If it starts with 44, add +.
4. If it already starts with +44, leave it.

Then check the length: 10 digits after +44 for nearly all numbers.

Written as	E.164
07400 123456	+447400123456
(020) 7946 0958	+442079460958
+44 (0)20 7946 0958	+442079460958
0044 20 7946 0958	+442079460958

Watch the +44 (0)20 style. It means "drop the 0 if dialling from abroad", and a naive cleanup that only strips brackets leaves +44020…. More on the general rules in E.164 format explained.

The Crown Dependencies quirk

Jersey, Guernsey and the Isle of Man use +44 but have their own ranges, and Google's libphonenumber reports them under their own codes: JE, GG and IM. We ran these through version 9.0.41:

Number	Reported country
+44 7400 123456	GB
+44 7911 123456	GG (Guernsey)
+44 7624 123456	IM (Isle of Man)

If your CRM only expects GB for +44 numbers, these look like errors. They aren't; they're valid numbers in the islands' ranges. Group JE, GG and IM with GB if you segment by country.

Ofcom's drama numbers

Ofcom reserves blocks of numbers for TV, radio and film, so fictional characters don't give out real people's numbers. They include ranges such as 07700 900000–900999 for mobiles, 020 7946 0000–0999 for London and 0161 496 0000–0999 for Manchester.

Validators handle these inconsistently. libphonenumber rejects 07700 900123 as invalid, but accepts 020 7946 0958 and 0161 496 0000 as valid landlines, because those are in otherwise valid geographic ranges. If a lead list contains them, someone typed in an example number.

What a UK check can't tell you

• Whether the number is in service. Disconnected numbers stay in valid ranges.
• Whether a mobile was ported. UK numbers can move between networks and keep their prefix, so the network name isn't in the number.
• Who answers. Only calling or a confirmation text does that. See how to check if a phone number is valid.

Validating a list of UK numbers

Upload a CSV on the SimpleVerifier verifier. Every row gets phone_status, phone_e164, phone_country and phone_type. Numbers without a country code are read as US numbers, so for a UK list make sure every number starts with +44 before uploading. Replace a leading 0044 with +44, and a leading 0 with +44; a number like 07400 123456 with no country code would otherwise be read as an invalid US number. Phone validation is included in the $29.99 plan, and any email column in the same file gets a live mailbox check.

UK lead lists come with their own rules for email outreach, covered in PECR and UK cold email.

Related: clean phone numbers in a CSV · mobile vs landline lookup