I am in need of some travel advice flying in and out of London.

We arrive into Heathrow on a Sunday morning this Summer. The same day we are heading directly to Venice, Italy. I haven't booked the flight from London to Venice yet. There are cheaper flights to Venice out of Gatwick, but I'm a little concerned with the timing.

We arrive into Heathrow at 9:15am. The flight from Gatwick to Venice is at 1:15pm.

How much would the transfer cost, and would I have time to make the flight?

There is an option to fly out of Heathrow, but it is much more expensive. Also, we land on a Sunday, so maybe traffic won't be too bad.

I appreciate any opinions or feedback. Thanks.

We were considering a similar thing, and we were told it is normally 45-50 minutes for a car service to go from Heathrow to Gatwick. You might consider contacting a car service directly-they should be able to give you better information for a Sunday. We ultimately decide with the additional hassle getting baggage out, checking in again at Gatwick etc. and then the cost the transport that we would rather connect through Heathrow.

I would ONLY do this on a protected booking. Never on separate tickets. If you arrive just a little late, or if your plane doesn't get a gate right away, or if your luggage is delayed, or if there is a long wait at immigration, or if there is a wreck on the M25 . . . if any of those happen you are totally SOL.

The time a car service would take is the LEAST of your worries. A car service would be a little faster than the express coach because you don't have to wait for the next bus -- but would cost much more.

In a word . . . DON'T

Meant to add -- If you are thinking of one of the budget carriers out of LGW -- they are generally VERY strict about check in time. So it isn't merely a race to get to the airport before the flight closes - you must get there before the cut off.

If you miss the flight you then have to buy very high walk up fares IF any seats are even available.

I did it once. We were arriving from Vienna to Heathrow. Departing Gatwick to the USA with frequent flyer miles. (only biz option available that day with AA points). It was very stressful, even with having carry-ons only and booking a transfer car with British Airway. They lost our reservation. Only when I provided a copy of the prepaid confirmation number, they called for a car. We waited and waited at Heathrow. I though of eating our losses and finding the bus. But the car finally came. Then there is the dreaded M25. My heart was in my throat every time we hit some traffic. In the end, it worked out OK. We got the flight with plenty of time to spare.
But I promise myself never again. We had 5 hours between flights.