This place is located just outside North London, in Crew's Hill where all the garden shops are.
It's a little hard to find - at least for me it was - but it's worth a visit. Review below.
Really friendly and helpful. No pressure to buy. Happy to walk around with you; I suspect the guy I spoke to could have talked Bonsai with me for hours if I let him!
They offered for me to go back and see them if I needed help with pruning etc, and to take one of their classes if I was interested at some future point, but for now, "just go home and enjoy it for a while." Kudos to them on all fronts.
The garden there is indeed more of a nursery with lots of humidity and water spraying around, but that didn't detract from my visit. If anything, it showed me they were actively tending to their stock and showing it some attention.
They seemed to have a genuine interest in the products they sell, and were keen for me to get the right one for my skill level and experience. They were happy to show me the pricey (and really lovely) eye-catching stock, but swiflty steered me toward the more sensible purchase.
I walked out with a great looking ficus (not literally; I did pay for it) and lots of helpful advice and information, booklets etc.
Look forward to going back soon to get another.
(18 months on, the ficus is doing very well, and perhaps may need repotting this spring)