Word of caution:
I phoned Judy's number about midday today (Sun) and asked for a 3pm booking.
I was told (by the maid, presumably) that I could not make an advance booking but "could come anytime - just book 30mins before you want to come".
Needless to say, later when I'd driven to a place I could get to Harrow-on-Hill well within 30mins and eventually got through after a couple of attempts, before 3pm, I was told she was not free for a couple of hours.
So, be wary if you're coming from distance. At the very least, you could face a wait. But you might be lucky.