There is usually a line of Black Cabs outside waiting.
But, beware, these could be a bit pricey if you are going a long way. An option is to consider using Uber. Or, walk into Twickenham and get a mini cab. Or, walk to Whitton Station and use Bats mini cabs (probably the better option) - or call them and pre book.
[I had to edit the post as I accidentally misspelled "walk". The profanity filter didn't pick up my type :-) The original advice I gave may have got you arrested though.]