I'd forget transferring by cab. Per the London Cabs website, cab fare from LGW to Central London is 85 pounds, and from there to LHR is another 45 - 60 pounds.
I second the recommendation for the National Express Bus. Per their website, it's only 19 pounds/person for the transfer.
Last edited by ExitRowOrElse; Sep 25, 2007 at 8:46 pm