Internet speed

Since Virgin media started to increase the speeds have noticed that i get a lot of buffing and very slow speeds am talking 25mb to 45mb speed tests done on various sites considering what i am paying them.
Before they said they were going to increase the speeds i use to get 155 to 160mb with no problems
I live just outside Doncaster in South Yorkshire.
Would be interested if any body else has the same problem in the Doncaster area