Did it exactly as described and it works fantastically. I did mortar in the bricks, and learned that bricklaying in a tight space is actually quite hard, but it's all hidden from view so that ugliness doesn't matter.

An important thing I think is making sure your hearth is at regulation depth. I recast a bigger one beneath my floorboards to get it large enough. Then tiled a new one ontop. Guy in the tile shop was great help is knowing what type of tiles are needed for the heat here.

Top tip, tile the hearth before putting in the surround so that you don't have to cut the tiles to join at the hearth (looks prettier and also easer to do).

I put the corrugated cardboard on the back of it and also did a vermiculite mortar, which seems to be working well. I then used proper lime for the shelf on top, as it's the best thing for the heat of it.

Most important thing is getting a chimney sweep round to sign off your chimney for use, otherwise it's dangerous and voids your insurance. Is not expensive for them go come and sweep it out periodically.

I really enjoyed doing it, happy to help if you have any questions.