Bertie
At the risk of repeating my comments on other threads, you will not regret flying with Gennady Elfimov at Skytrace, <a href="http://www.skytrace.co.uk" target="_blank">www.skytrace.co.uk</a>
You will not find a better Yak 52 instructor or indeed aerobatics instructor, in this country. The Yak is thirsty (but then it boasts 360 hp) - anyone who has seen Gena's display will agree that the Yak can be flown with agility, finesse and startling grace.
Having said that, my business partner has trained with Alan Cassidy in the Pitts S2A and very highly recommends him. Naturally, Alan's reputation and record speaks for itself, being one the the UK's most successful aerobatics pilots.
Cheers