Area code 020 is used for London landlines, which have eight digit local numbers. Mobile phones (07xxx) and special-rate services (03xx and 08xx) use their own country-wide prefixes.
To call from abroad, use the country code +44 and the full UK number minus its leading zero. For example:
+44 is the country code for the United Kingdom,including England, Scotland, Wales, and Northern Ireland. Country code +44 also includes the Crown dependencies of Jersey, Guernsey (including Alderney and Sark), and the Isle of Man.
Dial your international access prefix (commonly '00', but many countries use other prefixes) in place of the + sign, then country code 44, then you drop the first 0 of the number you are calling. For example, Liverpool is area code 0151, but you dial +44 151 from abroad.
Mobile numbers begin +44 74xx, +44 75xx, +44 7624, +44 77xx +44 78xx and +44 79xx.
Non-geographic numbers charged at geographic rates begin +44 30x, +44 33x, +44 34x and +44 37x.
Non-geographic numbers begin +44 80x, +44 84x and +44 87x.
Geographic area codes for landlines begin with +44 1 and +44 2, including these:
London is area code +44 20
All of Northern Ireland is area code +44 28
Birmingham is area code +44 121
Edinburgh is area code +44 131
Glasgow is area code +44 141
Liverpool is area code +44 151
Manchester is area code +44 161
Some corporate numbers begin +44 55 and VoIP +44 56.
Numbers beginning +44 70 are personal"follow-me" numbers that can forward to almost anywhere in the world. They are regulated as premium-rate numbers by PhonePayPlus.
Numbers beginning +44 76 are for pagers (except +44 7624, which are mobiles from the Isle of Man)
Premium Rate numbers begin +44 90x, +44 91x and +44 98x.
Any number in any range might terminate on a landline phone or may be allocated to a VoIP service and answered in another county or Another Country.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
If you are asking about the International telephone dialling code, the answer is 44
Somewhere in the United Kingdom
+44 is the country code for the United Kingdom +44 77 is a mobile phone.
The country code and area code of Coventry, United Kingdom is 44, (0)24.
The country code and area code of Birmingham, United Kingdom is 44, (0)121.
The country code and area code of Cambridge, United Kingdom is 44, (0)1223.
The country code and area code of Scarborough, United Kingdom is 44, (0)1723.
The country code and area code of Northwich, United Kingdom is 44, (0)1606.
The country code and area code of Moscow, United Kingdom is 44, (0)1560.
The country code and area code of Hunstanton, United Kingdom is 44, (0)1485.
The country code and area code of Bicester, United Kingdom is 44, (0)1869.
The country code and area code of Barnstable, United Kingdom is 44, (0)1271.
The country code and area code of Basildon, United Kingdom is 44, (0)1268.