[recycled sixtie]

Be very wary of possible heavy traffic around Gatwick and Heathrow. Being an ex resident of the UK I know. For example I rented a car from Gatwick but was supposed to fly out of Heathrow. Traffic got so bad on the way to Gatwick I turned round and dropped the car off
at Heathrow.

Also be careful of driving ( the other side of the road) after a flight. 8 hours is not a lot time to do much travelling. I am not familiar with transit out of Gatwick. It is an intense uncomfortable air terminal and not as nice as Heathrow. Be on the cautious side and be at the airport at least 2 hours before departure. There are hotels close to Gatwick if you need a day room to hang out.