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

Despite what's claimed by some so-called "authorities" these Londons and Deccas are identical other than different labels and packaging. Stereophile has published a Decca order sheet showing X number of Deccas and X number of Londons pressed at the same time on the same presses.  

Arthur Salvatore has been mentioned.  Anyone with enough interest to have read this far should look here for more than you may have wanted to know about this subject:

http://www.high-endaudio.com/softw.html#Decca

I think EMI is more consistent than any of them not that they are the absolute best. Erato is another consistent label. DGG is the most inconsistent going from wonderful to crap. I am not a record collector. I am a music collector. I shop for the artist and or the performer and take whatever I get for quality. If they are really bad I'll just send them back. I sent one Rycodisc back 4 times before giving up. Rycodisc is the absolute worst. I do not buy used records although I can understand record collectors doing that. 
There are several companies now capable of manufacturing first class records and hopefully will continue to reissue important performances.