Lord Lamont said Mr Major refused to back his decision that the country had to pull out of the mechanism on the day dubbed "Black Wednesday".

Black Wednesday is believed to have contributed to Mr Major's election defeat

Mr Major continued routine meetings as interest rates were raised for the second time in a day to 15% and the Bank of England spent billions supporting the value of a falling pound, according to Lord Lamont's memoirs, which are being serialised in The Times newspaper.

Black Wednesday - 16 September 1992 - was regarded as costing the Tories their reputation for economic competence and playing a crucial role in them losing the next general election.

Millions of pounds lost

In his memoirs, Lord Lamont said he first informed Mr Major that interest rates had to go up to force up the value of the pound on the exchange at 1030 BST.

He then went back to his office to wait for the announcement.

He said: "When it came the pound did not move at all. From that moment I knew the game was up. I wanted to suspend our membership of the ERM as quickly as possible to stop the haemorrhaging of our reserves.

"I asked to see the PM at once. There was no reply from his office. The minutes ticked by and I was conscious that we were losing hundreds of millions every few minutes but there was still no sign of any meeting or any indication that there might be one."

Nervous breakdown

Lord Lamont said he eventually went to see the prime minister, but was kept waiting while Mr Major met backbench Tories and eventually came out laughing and joking.

He noted the repeated reports since Black Wednesday that Mr Major had a nervous breakdown as events unfolded.

But he said: "In fact, he was perfectly calm then and for the rest of the day.

"My criticism was precisely the opposite: he was far too calm and slow to make the difficult decisions needed. He seemed unwilling to face up the issues."