We will fly to Gatwick in September and need to take a train to York. We will arrange a car rental prior to leaving to drive from York back towards London. We have never ridden the trains, other than the Express from the airport to London. Is there regularly scheduled service from London to York, or do we need to make arrangements in advance?
Do you wish to go directly from Gatwick to York? If so, take a First Capital Connect train from Gatwick to Kings Cross Thameslink, walk to London Kings Cross, and take a GNER train to York. Booked far enough in advance, fares are as low as 21 GBP. Walk-up fares will be 82 GBP and up. See the timetables and fares at www.nationalrail.co.uk.
If you take the Gatwick Express into London, catch the Tube at Victoria to Kings Cross. You can catch the train to York there. It is a beautiful trip. I'd even suggesst you consider NOT renting a car. We always travel by train in the UK and absolutely love it. It is easy, convienent and cheap when comparied to the cost of the rental, insurance, astonomical gas prices and parking in really INCONVIENT places. A BritRail pass is worth the cost and they come in several configurations (ex. travel 8 days out of 15 or 3 out of 8, etc.....)
There are sev trains per day from London-York; on the non-stop, you won't see as much countryside because it goes so fast. Countryside around York is beautiful for when you have your car. Thirsk, James Herriot's town, is abt 10-12 mi nw of York. His book, James Herriot's Yorkshire, has lovely photos and maps w/ descriptions of many of the small villages. Will this be your first driving experience in Britain? We've found that it's easier to adjust to driving on the opposite side of the road if one of us only drives and one navigates rather than trading off as we do on the Continent. My first driving trip, I printed "American Driver" on two 8x11 pieces of poster board and put one in the front and rear windscreens---had lots of good conversations when parked and many laughs and thumbs up when in traffic---at roundabouts, most cars would give way and let me in without honking/flipping me off.