I was fortunate enough to be invited to a Renault F1 test at Duxford Aerodrome last year. There is very little testing allowed in F1 now but the teams do a number of straight line test during the season. Last year Renault conducted these at Duxford Aerodrome near Cambridge.
Duxford is also a great place to visit as it is home to the Imperial War Museum and has many stunning displays, both indoors and outside. You also have the opportunity to have a flight in either a Tiger Moth or a Dragon Rapide, we chose the Dragon Rapide. Well worth a visit, check out their website. http://duxford.iwm.org.uk/server/show/nav.55