I actually find early summer to be the best time to rent a property...go figure! I suppose if it was student accommodation there might be a problem.
I'd say Bacchus is right and the landlord is following the Daft report. Perhaps you should have a chat (not argument) and see if you can reach a compromise. Interest rates have shot up for all this year and it's not neccessarily a landlord's greed which necessitates the rent rise.
Very often advice is given that you will find another place easily and perhaps this is the case, I don't know. However, although you're a good tenant, and the landlord should definitely appreciate that, you also obviously want to stay where you are. In that case, I think a compromise on the rise in rent is the best option.