Still have to charge 20% to customers though which is a very big hit for them £4 increase on 20 pound house.. or take that hit your self
No, not really. You are only paying the vat man 12% of your turnover, so you only need to raise your prices by 12%. Yes you are right in that the vat rate is always 20% on sales, but you still only raise your prices 12%.
For example, say you have your £20 house, and you vat register on the 12% flat rate scheme. Each time you do that house you now have to give 12% to the VAT man, so you only put your price up to 12% of £20 = £22.40, which is not too big a hit.
So in order for you not to lose any money, the prices only have to go up by 12%. Its designed to take into account the fact that some businesses (like cleaning, and other services) dont buy much stuff for resale.
I know a mate who has done this and he said it works out fine, and is easier from a paperwork point of view than keeping track of every single purchase you make.