Where is in UK area code 020 3286?

02078 is not a real UK area code. 020 is the area code for London, The number will be (020) 78xx xxxx. The '78xx' part can identify which exchange it is.

As the first digit is a "7" there is a good chance that the number is located in central London rather than an outer suburb - especially if the number was issued pre-2000 - although this is not guaranteed.