When I bought a house in Chiswick, West London, I knew it needed major renovation work – what I didn’t realise was that a miscalculation on the bathroom would end up costing me £45,0000.

With years of experience in construction and renovation, I wanted to make some major improvements to the three-bedroom Edwardian house when I moved in 15 years ago.

There were plans to convert the loft and create a large master bedroom, put in new wooden flooring, and restore the original features that had been ripped out.

But the project I was most excited to get started on was turning the smallest bedroom into a really grand bathroom.

I took out the ugly double-glazed window and created a big circular window, about seven feet in diameter, installing blue filtered light outside it so a night-time soak in the tub would feel like you were bathing in moonlight. Then I created a large dais under the window and on it installed a cast-iron bath.