are "LONDON" pressings made in the UK, inferior to the Decca pressings

@lewm , I'm not sure about the Decca - London situation in the late 70's. Perhaps Decca had changed their export policy by then. I do know that the New Malden pressing plant in the UK was shut down completely in the early '80's and Decca's were pressed in Holland by Philips (something to do with the take over by PolyGram I think).

Edgeware, thank you for sharing your wealth of knowledge of the subject. It’s possible that I am thinking of US pressings under the London label, and that would explain a lot. I will go through my collection and see what I have here because I still have anything I ever bought.

I was taking an electrical engineering degree at Imperial College in London during the early 1970's and I had the opportunity to work for Decca at their New Malden plant during one summer vacation, basically acting as a gopher in the pressing plant.
I can state categorically that the same stampers were used for both the Decca and London pressings at that time and the requests for metalwork often included both the US and UK labels in the one invoice- which explains why both issues often have the same stamper codes in the inner section.
I know of at least one copy of such an invoice which definitively proves that there is no difference.

Having said that, I have numerous copies of both SXL and CS issues of the same work and more often than not the SXL issues- most of which I acquired in the UK- sound better than their UK pressed CS counterparts- most of which I acquired in the US. The reason for this is entirely unclear, except that my SXLs were bought new, while the CSs were used.
US pressings of CS issues are generally inferior and are not worth having.
Phillips pressings can be quite excellent.

@wynpalmer4, thank you so much for sharing this information. It really is most valuable to get first hand confirmation that UK pressed SXL and CS labels were created equal by someone who was actually there!

But in your experience the SXL's are still often sonically superior. I'm sure this will delight the SXL fundamentalists, even if the reasons are unclear. In your case 'new versus used' might go along way to explain this. Another possible explanation could be that with each pressing run the first part was given the SXL label, while the latter got the CS label. In that case the slightly more used stampers for the CS labels might explain a slight sonic difference in favor of the SXL's. But this is pure speculation on my part and it's probably not very likely that Decca would stop halfway a pressing run to change labels. Having been there, can you shed any light on this? 

I've never been able to detect any generic difference between UK pressed SXL and CS labels with the same lacquers and stamper codes. In some cases the SXL sounded better, in others the CS. Because all my copies are previously owned, I tend to attribute these small sonic differences to their past playing history. This will always remain 'the great unknown' in collecting used records.

i cannot hear difference