The national guidelines state that you're supposed to limit ANY travel that isn't necessary, though. So, traveling from London to Liverpool in order to attend a football match isn't really on.
As it stands, though, I suppose this (like many other things) will have to depend on people using their heads. If you do travel from London to Liverpool in order to attend a football match, you won't be targeted or stopped by the authorities.
ETA Not the best example as per current tiers/levels. But you get the idea. London to Manchester, then.