I made a stupid mistake on my own house rewire that I only found out last weekend. The rewire had been done over quite a long period working around other trades and waiting for various walls to be boarded etc, so I was relieved when I'd got the final long run of cable in for the kitchen socket circuit back to the consumer unit. Last weekend I finally got round to connecting up the last two kitchen sockets, got to the last cable and thought, funny this seems quite flexible. Started to strip it and noticed grey, black brown. Went to the other end of the house to the consumer unit to check the other end of the cable waiting to be connected and realised I'd used 1.5mm 3core T&E instead of 2.5mm. FFS.
Luckily the plasterer hadn't been able to get to plaster the boards that the cable was behind, nor had the carpet fitter been yet. Phew. It only took a couple of hours to replace it and I learned a valuable lesson - read the label - twice at least, and check the end of the cable before you start!