You would need to quote the next two digits in the sequence to get an answer to this question. '020' is the code for London and the next 4 digits would identify the area in London.
Also, many of the newer prefixes in the UK are "virtual prefixes," meaning that they are not attached to a particular district within the relevant area code. Furthermore, with number portability, any specific 020 number could be located anywhere within the greater London 020 zone.
According to the BT web-site - the code does not exist. Numbers beginning 020 usually relate to London.
The context for your question is unclear. Please rephrase your question.
In the UK, area code 020 is London. It is an ordinary geographic area code, not a toll-free code. '34' would be the first two digits of the 8-digit local number in London. Other countries may have domestic area codes like 02034.
020 is the code for Greater London. London numbers have 8 digits after the 020 area code and begin 3, 7 or 8. The next four digits after 020 may or may not identify which area of London the number belongs to. However, with number portability, you cannot reliably pinpoint the part of London that a particular number is from.
In the UK, area code 020 is for landlines in London. 84 would be the first two digits of an eight-digit local number.