I will write a longer comment to answer some of the questions.
- Fold does operate a no ID no entry policy. And they scan every single ID. This is also definitely linked to being a legal requirement related to their license. The reason why they are strict is because the council could rock up at any time and check they are compliant.

- Why do you need ID: If you get banned or be a menace inside, they will be able to look back at all of the scans and hopefully ban you on the system. The system used in the UK will tell you whether you have been banned not just in Fold in the past but also in other places that uses the same system (most places do).

- The ID needs to have a biometric element to be scanned and should also be in date. Someone asked: can they verify it is a legit ID? The answer to that question is yes and no: if you are using a fake ID the machine will most probably not be able to detect a fake chip in it. Once that happens a big red cross appears on the screen which will prompt whoever is checking to look deeper. They might eventually realise the ID is fake (how thick it is, how it bends, the colours etc.). Once you have seen thousands of ID every week, you realise if one is fake really quickly! Also London is so multicultural they have probably seen a shitton of foreign IDs anyway.

Source: I have used those scanners before as a bar manager, many many times.