1) Some supply authorities supply a switch but in most cases the fuse needs to be removed as officially this has to be done by supply authority some are more strict than others your local electrician will know how best to deal with them.
2) Fitting a consumer unit comes under Part P and depending on where you live this could be a problem.
3) Once fitted the whole installation will require inspecting and testing this will require special instruments which are expensive.
4) The earthing arrangements are often substandard and when either the supply authority or building control arrive on site they could refuse to allow you to switch on if not up to scratch.
I would first go to projects page and follow links to Part P down load the free PDF and quickly read. Look at the questions you need to answer on sample forms on page 23 onwards also you may want to have a quick look at 17th Edition as well. If you are going to DIY there are forms available from the IET website without Web Version written across them and to new 17th edition but see what you think first I think you will find not quite as easy as it first looks.
Also with RCDâ€™s on nearly everything even electricians are having problems where they highlight other faults and it can turn in to a big job.