As with all road travel it all depends on the amount of traffic and the time of day you go, I did that trip last month and it took me 2hrs 50mins but it was stop and go on the motorway then I hit the rush hour traffic.
At normal speeds and conditions Central London to Liverpool Pier Head should take around 3 hours 20 minutes, but obviously there are variables like weather, day/night, comfortable driving speed etc which could alter things slightly. That's for a journey of 210 miles.