So what I have done before is I have designed the install, you put where you want the sockets, I mark out all the chases, I say what boxes I want, I tell you what screws to use and grommets.. You cut all the chases and fit all the back boxes.. I then with you run in all the cables, you do all the capping (I then test), and fill the chases.. If you are competent ill let you do some of the second fixing but leave like the sockets off and ill check before letting you screw them back, then I test and certify, only I do the board...
This can save a lot of money by working with a sparky and I personally don't see the difference between that and having an apprentice or someone work with me..
I have worked with people who have said they have done "part P" and are 17th or 18th edition qualified and they do really basic things wrong like diagonal chases..
Your big danger if you go down the route of building control is if they find any issues or anything they don't like you either have to try and find the fault/fix it or redo parts of it..
The alternative is don't buy the house if you can't afford the house and to make it safe, sorry to be harsh but I am guessing its cheap because it needs things like a rewire... Bottom line though to answer your question no self respecting sparky is going to want anything to do with signing off your work, its just too much risk for basically no reward... Your asking someone to sign to say they designed it, constructed it and tested it and take all that responsibility when they didn't do it... Much better to work with the electrician so you do the grunt work, will still not be cheap but then a rewire will never be cheap, especially with the price of materials at the moment.