Next May I am landing at Heathrow on Virgin Atlantic. Will three hours be enough to exit the plane, go through Customs, take a bus to Gatwick, go through Security and make my flight or am I being optimistic?
Are you on a single ticket or are you buying a separate ticket from Gatwick to your final destination? On a single ticket, 3 hours is technically the minimum connection time between LHR and LGW. Personally, I would avoid a route with so little time. If you are buying a separate ticket from LGW, don't even attempt it.
Steven, I think that's a bit "optimistic" and doesn't allow for unexpected delays (ie: takes longer getting through Passport control, transportation between airports doesn't move as quickly as anticipated, etc.). In the same situation, I'd probably want to allow slightly longer. I'm sure Nigel or one of the others from the U.K. will have some good suggestions. I assume you're connecting with one of the budget airlines at LGW? Cheers!
Into Heathrow on Virgin. Onward from Gatwick on BA.
I can't see it happening unless you can time-travel. Figure 90 minutes from touchdown to entry into Heathrow airport public areas. Figure an hour by road between the two airports. Figure 30 minutes making the connection onto and off the bus/taxi, etc. A minimum of 2 hours check in time at Gatwick for a domestic flght after you have found the check in desk at Gatwick. So, if all goes absolutely perfectly, that's 5 hours, a little more than you have.