RISHI Sunak has been accused of "gross mismanagement" after the UK's oldest independent economic institute found he had wasted a staggering £11 billion of taxpayers’ money.

The National Institute of Economic and Social Research (NIESR) said the Chancellor’s failure to insure against interest rate rises had resulted in unnecessarily high payments, which have cost the taxpayer billions over the past year.

The institute’s director, Professor Jagjit Chadha, said that Sunak’s failure to act had left the government with “an enormous bill and heavy continuing exposure to interest rate risk”.

The think tank said that neglecting to insure against the risk of rising interest rates was a “lost opportunity” and was “an unnecessary cost to the public finances at a very difficult time”.

Sunak’s inaction amount sto “gross mismanagement”, according to SNP shadow chancellor Alison Thewliss MP.

She said: "While households struggle to make ends meet as the Tory-made cost of living crisis spirals out of control, the Chancellor is piling on the hardship with his gross mismanagement.

The National: SNP MP Alison Thewliss said Sunak's inaction amounted to "gross mismanagement"SNP MP Alison Thewliss said Sunak's inaction amounted to "gross mismanagement"

“At a time when ordinary people need strengthened support to properly tackle record levels of inflation and rising fuel and energy bill prices, Rishi Sunak’s blundering, arrogance and incompetence is instead leaving them to pick up the multi-billion pound bill.

"The Chancellor's failure to listen to the advice from experts like NIESR has cost us all dearly.

"There are serious questions to answer for the Chancellor over how the public has been forced to pay an eye-watering £11 billion because of the steps – or lack of – taken by the Treasury."

It comes as research from the Centre for European Reform (CIR) showed that by the end of last year the UK’s economy was 5% smaller than it would have been had we still been members of the European Union.

CIR’s figures showed that this amounted to around £31 billion.

SNP president Michael Russell said that the Scottish Government’s original estimate of how much money Scotland was set to lose from Brexit now looked “optimistic”.

He tweeted: “Comparing these figures to original @ScotGov estimate of “up to” £11 billion loss to Scotland caused by #brexit by 2030, it would seem that the Dec 2016 forecast was optimistic.

"More likely hit is now in excess of £14 billion”