In the last 10 years I've seen ....
Mistress Louisa in Hertfordshire (now retired, I think) - that was quite a long term one; due to closeness of work, probably saw her once every 6-8 weeks
Mistress Sandy, also Hertfordshire
Mistress Paris, Sandy
Didn't really think much of the last 2 to be honest, so looking for some recommendations in East England
Out of East of England, there's been...
Mistress Jane, Reading
Madame C, Farnborough
Miss Alice Silk/Nanny Alice, Kensington.
Been to the London Retreat a few times