Got your pm but can't reply on iPhone - have a mobile number will send it to you tomorrow though can't remember his name! Other one to try is fishlock stables he does arenas too, number is 01945 701131 (Gary fisher - tell him Ian and Abby recommended him!)
We used :
Walnut Tree Farm
Phone Number: 01638781794
6 years ago now - excellent arena - never puddles apart from during a proper downpour and is gone within 30 mins.