Knowing that, I've always been "on the lookout" for R. Luxembourg on my trips to London. During the daytime, whatever signal there is is quite weak in Central London. At night, 1440 is rather clearly audible, but it doesn't exactly blast in. It's tough to identify, because apparently what's happening (and I stand to be corrected) is that R. Luxembourg is doing what goes on quite a bit in shortwave broadcasting. That is, leasing their facilities in blocks to other countries' international broadcasting operations.
There are also two other possibilities that may explain why R. Luxembourg (or whatever this is on 1440) doesn't come roaring in as might be expected at night and is all but invisible during the day....
First, London has its own local blowtorch on second-adjacent 1458. 300kw if memory serves, and it does splatter. I'm unclear to what extent the overall effect is on 1440 in southeast England. Secondly....I'm wondering if R. Luxembourg is using a different DA than in its days as a top 40 powerhouse in the '60s. The UK may have been the target then, but the continent might be more desirable for them now. Also, I'm wondering if London's 1458....a commercial operation....even existed "back in the day".