here is my test as of this morning, bare in mind on friday it was at 23meg
Sky don't give you better speed, the exchange does this automatically.
The longer a connection stays up, the better the exchange regards the line and will gradually increase the speed up to the max it can achieve.
If a line keeps dropping, the exchange sees a problem and reduces resources to that connection.
Some people turn all their equipment off at night and this is the worst thing to do for a broadband connection as the exchange sees the turning off as a problem.