"(1) Where a person has (whether before or after the commencement of this Act) paid an amount to the Commissioners by way of VAT which was not VAT due to them, they shall be liable to repay the amount to him. (4) The Commissioners shall not be liable, on a claim made under this section, to repay any amount paid to them more than three years before the making of the claim… . (7) Except as provided by this section, the Commissioners shall not be liable to repay an amount paid to them by way of VAT by virtue of the fact that it was not VAT due to them"
" Origin and scope of the right to deduct 1. The right to deduct shall arise at the time when the deductible tax becomes chargeable."