Unless you are a very experienced builder, you should not attempt to manage a building project on your own house by yourself. The most important thing about the project is that it runs smoothly. You need to try and hit your posited time scale and try to stay within the limits of your budget. These are such important considerations that it makes much more sense to have a professional on board to help you achieve them.
Professional project management is a real asset because it brings experience to your project. The communication between those working on the project is likely to be much more efficient with a professional project manager involved because they are experienced in dealing with tradesmen and they have a deeper understanding of the stages that go into the completion of small scale and large scale renovations.
When your London home seems to be in need of renovation, instead of tackling the management of the project yourself, speak to professionals and see what they could bring to the table. If they are also in league with a team of tradesmen and designers then you are in luck because your project is even more likely to go well under these circumstances.