This isn't a London code. It is the area code for Brentwood in Essex which is about 30 miles northeast of London.
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.
London's telephone code is 020 followed by an eight digit number which will start with 3,7 or 8. The number that you have asked about is not a London number as you have described it.
The telephone code +44 20 is used for London, United Kingdom. The "+44" is the country code for the UK, and the "20" is the area code specifically for Greater London. This code is used for both landlines and mobile phones when dialing to or from the London area.
The country code and area code of Brentwood, United Kingdom is 44, (0)1277.
UK telephone area code 020 is London and surrounding areas. It is not possible to narrow down the location any further with the information given. Furthermore, with number portability, any specific 020 number could be located anywhere in the greater London 020 area.
The London phone directory no longer lists London telephone areas. All that can be gleaned from the given number is that 020 means that it is a London number and 8578 is somewhere in the outer London area.
020 is London. 020-3 numbers can be anywhere in London. The operator who "owns" this number is Frontier Systems. Note that the area code for London is just 020, not 0203 or 0207 or 0208.
In the UK, telephone area code 020 is London. A number beginning with 020 3432 is a "virtual" number that could be anywhere in London. Furthermore, with number portability any specific 020 number could be located anywhere in the London area, served by any local phone company.
The country code +442 is used for the United Kingdom, specifically for telephone numbers that are part of the London area. It is primarily associated with landline phone numbers in London. In general, the country code for the UK is +44, with the '2' indicating the specific London area.
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.
There is no telephone area code 185 in Russia.
There is no area code 0208 in the UK. The area code for London is just 020, with 8-digit local numbers. A number beginning with 020 8749 is most likely a BT landline in Shepherds Bush, but with number portability any specific 020 number could be located anywhere in London, served by any local phone company.