All mortgages in Britain will be in effect graded and the least risky will be given an official seal of approval under plans designed to reopen the market for wholesale mortgage financing to be unveiled in next week’s Budget.

Alistair Darling, the chancellor, will publish plans that will see a “gold standard” kitemark for batches of mortgage-backed securities that comprise only those loans that meet higher standards of creditworthiness and quality thresholds.