EGLL only makes sense for a business jet if your PAX are interlining onto a scheduled flight. For the west end of London (which would make sense if you were looking at LHR)
If you don't mind paying a bit over the odds and need to be in the west end in minimum driving time, and aren't planning on hanging around too long - then use Northolt.
If you are planning on staying for a while then Farnborough works out okay'ish (but Farnborough is a boring place to be for crews)
If you are planning on staying a while but haven't got a massive budget and you have the performance (and your PAX don't mind an extra 15min into town) then Oxford works (M40 to M25 takes about 35min, Knightsbridge doable in 1hr 15min)
If you're going to Canary Wharf or the Square Mile, Biggin or Luton work OK.