Bag the Gatwick and/or Heathrow Express and any and all train travel in the UK. Too bleeding expensive. Try National Express buses. Among other things, Nat Ex does fast buses from all London airports to center of town -- to Victoria bus terminal (next to Victoria rail terminus) and/or Golders Green if you are going to North London. As an old fart of 62, I pay only five quid for the bus, versus 15 or so for the train. Young farts pay less than 10 quid.