The SkyDemon chart will usually be more accurate than the printed CAA chart. The main reason behind this is that it's updated every 28 days, at which points airspace DOES change in the UK, though usually not significantly.
Another reason, the one apparent in this thread, is that the UK is full of such a needlessly complex system of class A airways and other miscellaneous "fillets" designed to complete the airway jigsaw puzzle. Last year it was pointed out that Y53 extended much further than the CAA chart showed, and the SkyDemon chart correctly depicted it. Anyone depending on a CAA chart (whether printed or used digitally in another product) wouldn't have seen that bit of class A. SkyDemon works by taking the raw route structure (as specified in the AIP) and constructing the airspace chunks out of it, whereas the printed chart is produced (presumably) by a person drawing lines and trying to fit them together in a way that is aesthetically pleasing.
I hope this explains what you're seeing and the discrepancy. I guess someone from NATS or the CAA will confirm where the discrepancy lies and what people should do about it. The printed 1/2mil chart is so ubiquitous that I can't believe people would be prosecuted for infringing a corner of class A that it failed to depict, but you never know.