If you want good value, don't look for it inside the M25.
I recently undertook a renovation project for a two bedroom property in West London which is owned by an investor with whom I've done multiple deals up in Manchester.
London is more expensive than any other UK city on just about every metric including hourly labour for building contractors. (I once made the fleeting mistake of thinking that the "day rates" for various trades published on the website of a well known London property maintenance company were somewhat reasonable, before realising that they were in fact quoting hourly).
So whilst I expected the cost of building work to come in significantly higher as compared to similar projects we have done in the North and elsewhere - I hadn't realised by quite how much.
I have completed multiple kitchen & bathroom remodels on properties in the North and East for c. £6k all-in including units, fittings and labour. I had five contractors quote for the job in London against the very same schedule of works. The labour alone was quoted from £13k all the way up to £23k. What a bargain. With yields on investment property in central London languishing around half of what you can get in Manchester and elsewhere, any return on capital employed will quickly be eaten up by the cost of maintenance and renovations.
Perhaps it's a result of the extreme imbalance between current demand and supply for such services - driven by the coronavirus pandemic and the consequent and much publicised boom in home renovation projects. Or perhaps it's just a reflection of what contractors can get away with in a neighbourhood where the average home price is approaching £2 million.
To summarise: if you want to make money investing in rental property, go North. If you want to make money fitting bathrooms and kitchens, buy a house in Slough and work exclusively for property owners in Kensington and Chelsea.