It's far less than 50% in many settings, bob. The tube seems to see most compliance. The buses are very hit and miss and it depends where you travel and at what time. Ironically Central London (which usually sees the busiest services) often sees little compliance whereas in the suburbs obedience is much greater.
On a wider note, I think every bit as important as vaccination is the entire issue of face coverings and it needs a proper examination. There are now children of two years old or possibly older who have no recollection of seeing any adults in many settings unless they are masked up and I imagine they believe it is quite normal. It can also lead to scenes like this:
https://twitter.com/456trainmama/status/1439209826668658688?s=21
I accept that this is in the USA and they may behave a little differently to here. But what sort of society thinks it is OK to force such a young child to wear a face mask, clearly to the point of causing it some distress? There are messages of support on that Twitter article (e.g. "Shame on mom for not teaching this child to wear a mask.") That mother - and a few others by the sounds of it - really need to get a grip.
The matter of face coverings was never a scientific exercise and decision but purely a matter of politics. This finally manifested itself perfectly in the House of Commons last week, with half the House masked up (the "good guys") and the other side naked (the "baddies"). The behavioural scientists have succeeded in convincing the population that they are being "kept safe" when in fact all they really are is "feeling safe" - a different matter entirely.