Can also recommend Gott & Wynne. Last time I went on a Track day was three years ago and it was a £100 increase in excess but things may have changed since then. The excess for TOTH was 10% of the cars value but no Extra premium in either case.
What you may find useful is that they will Insure drivers for a week at a reasonable premium and I have used this for my eldest son and rather more terrifying when I took my father to France a couple of years ago. Need to be 25 to get cover though.
