Agree with Loopy. I have fished happily at Avon Springs for 7 years now and the fish are certainly the best to eat that I have ever sampled. Also surprised that your fish didn't fight well, the ones I have been catching over the last 6 months have been absolute animals, and I use a 7 weight outfit and 6lb leader point so I don't aim to take any prisoners.
Take Loopy's advice and try a split river and lake day in May, June, September or October, the river beat is excellent for both trout and grayling.
Also remember the fishery has two lakes not just one, and the upper lake can fish very well indeed with opportunities for stalking later in the year. Somewhat surprisingly, to me at least, the feeding habits of the fish differ as between the two lakes, I have spooned more shrimps, hoglice, snails and corixa from fish in the upper lake, and daphnia and buzzers from fish in the one nearer the house.
And there's no fishery rule that you have to fish off the little platforms on the house lake.
Loopy's comment about customer service skills is superbly diplomatic

and I know what he means - but do persevere with the fishery and the people.