The Heathrow Express is the train from Heathrow to Paddington. What you want is the Speedlink Gatwick-Heathrow Transfer coach, takes an hour or so (but, as the web site says, allow much longer), costs around £17. http://tinyurl.com/2xrwl

The bus and train transfer suggested further down is cheaper and probably more certain, as the bus to Feltham is less likely to have traffic problems. So although it won't be as fast as the Speelink if Speedlink has no problems, it could still be faster.

Don't try the underground, terrible with luggage. And I hope it isn't a Sunday.

Doug Weller Birmingham, England