Re: distance from heathrow to gatwick?????
At last one post where i can give information and not just my opinion. After living in london for the past 8 months you learn very quickly how to get around the quickest and easiest way possible,
For the tube:
Depending on what terminal your leaving from, i would think 1,2,3, ( 4,5 only limited tubes so times will be different ) need to get on the piccadilly line ( cant go wrong it's the only line lol ) get off at hammersmith and then take the district towards upminster and your'll get off a victoria. Then you need to move to the over ground which is right next to the underground stop, follow the exit signs for overground cause there a few different exits and you could end up on the wrong side and have no idea where you are ( yep been there and done that ) Gatwick express is brilliant wish i could use it but wouldn't be worth my while going to victoria so i have to put up with stopping at every station, it NORMALLY departs from platform 17 but do check this cause it can change.
Time from heathrow to victoria 45-50 mins
Time from victoria to gatwick 30 mins (only on express, will take a lot longer not on the express, make sure you get on the right train ( yep again been there and done that, and missed my flight )
As for national express, they may say it only takes an hour but i think they can only do that at 3am in the morning!!!! Average time could well be 2 hrs depending on what time you are travelling.
For exact time go to
http://journeyplanner.tfl.gov.uk
Will give you information on all transport in london, over/underground and buses. If you select the advance button you can even put in the time you need to arrive and it will figure everything out for you, and also if there are any problems (as they are doing lots of upgrade work at the moment, mainly at weekends ) it will factor in those extra times as well.
Also if your going to be doing this often and you haven't already, get an oyster card, available at most newsagents, will cut down your tube/bus fares by half.