London Underground toilet map: https://www.tfl.gov.uk/cdn/static/cms/documents/toilets-map....

They are usually very clean, probably because people assume they don't exist.

Most of the central ones there are "cheating" by counting the toilets of the attached National Rail station. Aside from that there are hardly any in the middle. I must admit I was unaware of those at Piccadilly Circus and Green Park though - that will come in handy.

I lived in London for nearly 20 years and didn't know that any stations had toilets.

You should try the ones on the train from Mumbai to Panaji.

Otoh the food is amazing, just try not to imagine how the chef washes his hands.

To compare, smaller train stations in Italy also have squat plates. (Though the restrooms are satisfactorily clean.)