my advice....start with a direct line and dogleg it a bit to avoid difficult CAS. Sometimes it only adds a minute or two to avoid CAS rather than transit, although for you it'd be a good experience.
Go as high as possible and route down over Wales. There is virtually no airspace over Wales so you get get reasonably high. If you feel comfortable then transit a straight line from the end of the LL route (if you go that way) to Newquay avoiding the danger area in Wales. I'd go at 8000' once clear of the LL route. Easy peasy route.
Going via Blackpool and to N wales (avoiding Liverpool to the west) does not add any time to the route if you wanted to go that way. You could stay at 3.4k from Blackpool to Wales then you are free to climb to FL145 if you want.
I reckon it would take about 2:30 to 2:45 in a PA28 with no wind.