First, each UK circuit will have a permit that states how many cars are allowed to start a race. As an example, Snetterton, from memory is allowed 32. So grid sizes will always be small at some circuits, regardless of how many cars want to be on the grid.
Silverstone GP has probably the biggest 'allowance', and as Kipper says the U2TC grid at Silverstone Classic was huge last year. Only 33 finishers however! The Masters Masters Touring car race was slightly smaller with 48 starters, but managed 38 finishers.
So Silverstone Classic is the place to go if big grids are your thing.....
