Summer may be officially over but there’s still time to eat outdoors. TreeHouse@51 has the most wonderful courtyard to catch the last rays of the sun.

Somehow Treehouse@51 has escaped my notice up until now, possibly because it’s so wonderfully hidden in the posh part of London they call Buckingham Gate, and in fact Buckingham Palace’s back garden is close by.

It’s also just a few minutes from Victoria Station, but it’s another world. The Taj Hotel, all bi-coloured bricks and Days of the Raj external details (it was built in 1902)  quietly embraces its secret courtyard restaurant and doesn’t advertise it.

As soon as you do find it though, it’s a wow moment with a beautiful central fountain  depicting scenes from Shakespeare’s plays gurgling pleasantly away, matching the gurgling V8s of the supercars that now and then slowly pass by the courtyard’s exterior to drop off hotel guests and diners.

Inside is very special, it’s a glass dining room designed by Conran & Partners, but day or night the courtyard is the place to be when it’s dry weather. We looked up at lunchtime, saw no black clouds, so sat down.

Staff are remarkably jolly, mostly from India, the Taj is an Indian brand, and they are rather proud of their special space and with good reason. They also double as bird scarers, as in the daytime the occasional pigeon may try and join the guests.

There are two menus, one is Hotel Standard, something for everyone, and one is the Courtyard Menu which is far more interesting, particularly as it makes use of a Robata grill – a Japanese charcoal grill which burns intensely hot.

We have salads first, for P Bocconcini, Summer Squash Fettuccine, Sundried tomato, pesto, olives, balsamic drizzle, herb and sea salt. This was a bit underwhelming, the olives had seen better days, and the balsamic was everywhere. Unadvertised mini mozzarellas gave some interest, but overall it gave the impression of not being all that freshly prepared.

My own starter was more successful; advertised as Baby Roots, Edamame, Hass Avocado Red Quinoa and a berry yoghurt dressing, it wasn’t quite all that as the quinoa was the usual white version and there were no roots,  only a lot of soft fruits. This, with the berry yoghurt on the side, gave the impression that this might have been a breakfast dish repurposed.

Still the quinoa was well cooked, the beans and the avocado fresh and the berries excellent. It had a good summery vibe.

Mains were far better, with Sea Bass fillet  sumac, basil lemon and garlic confit, a bowl of well-dressed salad and just enough spicy chips. Lots of big flavours here, and a very decent bit of fish. Sumac elevates everything it spreads its sour wings over.

I was keen to stay vegan-ish so had to try the Spiced Tofu and patty pan squash,  Gochujang, This was really rather good, the Gochujang (Korean chilli paste) was fearsomely hot but that’s how I like it and it is always tempered by the sweetness that comes from the cooked glutinous rice that makes up the bulk of it. The patty pan squashes were the stars though, picked small they had taste, and not water, and the searing heat of the grill brought it all out.

This came with the same chips and salad, which was perhaps a bit lazy and made the table look a bit samey.

This was all good though, especially eaten al fresco, but the star of the show turned out to be the last act, a Mango cheesecake with a Chilli mango coulis.

The addition of chilli was what made this really work, quite a powerful bit of chilli as it happened, but it counterpointed and actually accentuated the deliciously sweet mango layered thickly on the thick biscuity bass. This was a luxury dessert.

Treehouse@51 is a luxury kind of place, not madly expensive but definitely stylish and with a kitchen that goes further afield than Hotel Restaurant and is unafraid to mix European and Indian styles to largely good effect. There were plenty more dishes I’d have liked to try.

Apparently that Mango Cheesecake can be served with afternoon tea in the gorgeous courtyard, and you’d be out of your tree not to try that.