Compared to what, on the streets? At music festivals, in town centres during the day, at protest marches, or any other events. I would say there are more police at events that are most likely to have trouble.
Take the last student protest march in the centre of London at the end of November, 2000 protesters and 4000 police. Now I do not think less than 100 police officers at a ground with 22,000 supporters is disproportionate.