I find routing up and down to the east of the class A airspace when IFR is preferable as you can usually get a radar service all the way even at weekends and it can be done at a sensible level above cloud. Class D clearances never seem to be a problem. I stay clear of class A. I would go CFD GAM then direct from about 30miles north of GAM.
The west is of course the more direct. SWB WAL but it's a pain to have to decend below class A at Liverpool and I'm not sure how accomodating Birmingham would be if you asked for a radar service. I would never attempt the Manchester low level corridor IFR. Going by WAL you would still be in gliding distance from land.
Also 60% of the time the weather is better in the east.
DO.