Essex is a fairly large county with different area codes for different towns. Examples include 01702 for Southend and 01245 for Chelmsford.
For an exact answer, you will need to search for a specific town within Essex.
Clacton-on-Sea, Essex, is in UK area code 01255, or +44 1255 in international format.
(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.)
01691
01931 is the telephone code for Shap, Westmorland (near Penrith in Cumbria).
UK telephone area code 0161 is Manchester, but 0161 553 is an invalid number block.
Clacton - UK Parliament constituency - was created in 2010.
UK telephone area code 01954 (or +44 1954 in international format) is Madingley, Willingham, near Cambridge.
A UK telephone number beginning with +44 754 is a mobile.
Until the early 1990's, area code +44 21 (or 021 within the UK) was Birmingham, which is now area code +44 121 (or 0121 within the UK). There has never been an area code +44 217 (or 0217) in the UK.
01792 is the area code for Swansea
In the UK, area code 020 is London, but there are no numbers beginning with 020 2. Other countries may have similar telephone area codes.
UK telephone area codes were first assigned in 1958.
UK area code 020 is London, but there are no valid numbers beginning with 020 4, much less 020 43. Also, the area code for London is just 020, not 020x or 020xx. There are no other UK telephone area codes beginning with 020.
00 + 1 + Area code + telephone number.