ideally for me at least ale should be served at 11C all the time. Some benefits from warming a tad, most is best served around there. Plenty of lager and a few others are better served cooler, about 8C imo.
I hate warm beer, sadly I've had too much of it in London and I suspect that is what has contributed to the myth that british beer is served warm and flat. That is the place that 95% of tourists go to and they got (I know it has improved a lot over the last ten years or so) shite beer. It's so much warmer in London than it is in the north or scotland