The Chancellor of the Exchequer has doubled the inheritance tax threshold for civil partners and married people.

Presenting his pre-Budget report to the House of Commons, Alastair Darling announced that from today the threshold will rise to £600,000. By 2010-11 the threshold will rise to £700,000.

Until now all estates worth more than £300,000 were taxed at 40%, although assets left to a civil partner or spouse are exempt from taxation.

Civil partners and married couples can combine their allowances after their one of them dies, allowing the remaining partner’s estate to be tax-free up to £600,000.

The new threshold will be backdated for three million widows or widowers, meaning that those whose spouse or civil partner predeceased them will still see their estate be tax-free upon their death up to the £600,000 limit.

However, as civil partnerships only became law in December 2005, it is unlikely that this backdating of the new threshold will benefit many civil partners.

Mr Darling’s first pre-Budget report as Chancellor saw him pledge to target “non-dominciles” and change air taxes to flights and not passengers.

At last week’s Tory party conference the Shadow Chancellor George Osborne unveiled plans to raise the inheritance tax threshold to £1m and to target “non-domiciles,” wealthy foreign nationals who live in this country but pay no tax on money they make abroad.

Mr Osborne said that today’s announcement was a stunt and that the government had stolen Tory policies.

“This is not leadership of this country. It’s followership, Prime Minister.

“It’s not strong, Prime Minister. It is weak,” he told MPs.

“We all know that this report was brought forward so it could be the starting gun for the campaign, before the Prime Minister took the pistol and fired it into his foot.”