Interest runs from the date the tax should have been paid. See SDLTM85930
Interest is regarded as commercial restitution to the Crown made for the purpose of making good a loss of tax. It should not be regarded as punitive to the purchaser.
Interest is payable without deduction of tax and is not allowable as a deduction in computing income, or profits or gains for tax purposes.
The rate of interest is fixed by statutory instrument and is the rate applicable under FA89/S178.
Bankruptcy and liquidation
Interest under the Taxes Acts ceases to run when a purchaser becomes bankrupt or an insolvent company goes into liquidation. Any interest for the bankruptcy or liquidation period will, if there is a surplus, be paid under the bankruptcy legislation or the Companies Acts.