That's an incomplete code. You need one more digit.
From outside the UK, replace the trunk prefix 0 with country code +44.
(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, and many other countries use different prefixes.)
Leyburn, Wensleydale
There is no city in the UK starting with area code 791. All 'area' codes starting with 7 are mobile (cell) phone numbers.
It all depends on what area of England you want ! Each area has a different code, there is no code for England itself.There are many post codes in England, so it depends on where you are writing to. The post code is only one part of the address. You need to know it all.
01883 is Caterham which is just south of London in the county of Surrey.
UK area code 01752 (or internationally +44 1752) is Plymouth.
Redwood City is in area code 650.
01942 is the area code for Wigan and the surrounding area. Wigan is located in Greater Manchester, in the North West of England.
Missouri City is in area code 281, with overlay code 832. There may also be some Missouri City numbers in area code 713.
Rockwell City, Iowa, is in area code 712.
Traverse City, Michigan, is in area code 231.
The area code for the whole Davao City is 082.
Johnson City, NY, is in area code 607.