Hi! I would advise this to anyone looking;
Most credible, accredited building companies will exceed the vat threshold, furthermore, some points.......
For a large scale project involving construction work on your house your builder should offer some insurance-backed guarantee covering structural integrity and water ingress.
carry out due diligence and check on the company's and directors' history - companies house.
It can be very tempting when launching a project to be pulled in on price, but please check history - ask for references.
If the architect's recommending, check this out (they can be commissioned in some instances - it's a grubby old business!)
Be careful on giving large deposits, better is to pay frequently rather than big lump sums in advance.
It also comes down to your trust and confidence with the directors, choose on person as well. Get commitments from them in terms of time they'll put over to your project..
Hope that's useful, all the best