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

i cannot hear difference

First off one big difference is a lot of changers in use in US, not the case in UK. Also many times the Decca LP was put out first, so more likely to have fresher stampers. Charm has all the details on which LP came out first for most titles:
http://www.charm.rhul.ac.uk/discography/decca.html

This is the main document at Charm:
http://images.cch.kcl.ac.uk/charm/liv/pubs/DeccaComplete.pdf

Here is a sample entry:
>0974
Pr: James Walker (m) Eng: Kenneth Wilkinson (m)
Pr: Erik Smith (s) Eng: Cyril Windebank (s)
15-16 Jan 1957 Kingsway Hall
Ruggiero Ricci (violin), London Symphony Orchestra, Pierino Gamba
BRUCH Violin Concerto No.1 in G minor Op.26
MENDELSSOHN Violin Concerto in E minor Op.64
(Jly57) LXT5334 = (Aug58) SXL2006;
(Sep57) LL1684 = (Sep58) CS6010, (May89) 417 793.2DM.

Here we see SXL2006 in August of 1958 versus CS6010 in September; advantage to the SXL.

Works like a charm for collecting Decca/London!

I'd lean towards SXLs because the LP was more likely played by a good turntable and needle. In the US YMMV with lots of people having nasty changers and needles plus poor LP hygiene habits. Very pleased with British dealers and the quality of their LPs.

I have thousands of records many London i have always found the Decca to have better sound even though they were pressed in the same plant.Go figure.

i have both Deccas and Londons and for the most part, they seem to sound about the same.

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.