Right, I did it this way through my builder last year. His Dad is a financial advisor and the VAT registration threshold is £81,000 and easy to avoid if a builder wants the money for any goods bought to be paid directly to the merchant.
So I had a quote, it detailed all the companies who would be supplying their goods or services. The build started, I paid the digger guy directly, and the chap who took away the soil. The builder then ordered the stuff needed for the foundations from the builder's merchant who he has been using for decades.
He gives me the details of the cost, I ring the merchants, pay them and later the same day the goods arrive. At the end of the week the builder invoices me for his service (labour) and I pay him directly into his bank account from mine.
I paid the concrete man, the window and doors people, plasterer, roofer etc directly to them and I get receipts for what I have paid.
I do find this very interesting the way people view tax avoidance and tax evasion, how many people have an ISA or see no problem with an ISA, a savings account with no TAX!