LONDON — Britain’s main political parties agreed Thursday to grant Scotland new tax and spending powers to fulfill a promise of greater autonomy made as politicians scrambled to persuade Scots to reject independence in a recent referendum.

The plans are unlikely to satisfy hard-core Scottish nationalists, but could have far-reaching consequences, taking Britain toward a looser, more federated state.

In a Sept. 18 referendum, 55 percent of Scottish voters opted to remain in the United Kingdom, while 45 percent voted to leave.

Since then a commission of politicians from Scotland and the rest of Britain has been thrashing out proposals to fulfill the promise made by anti-independence forces in the final weeks of the campaign, as polls showed rising support for separation.

A plan published Thursday would give the Edinburgh-based Scottish parliament, established in 1999, the power to set income tax rates and keep the revenue in Scottish coffers. Scotland would also gain new control over welfare spending.

Prime Minister David Cameron said the proposals kept a promise he’d made during the referendum campaign, “that a No vote did not mean no change.”

But John Swinney, deputy leader of Scotland’s pro-independence administration, said the powers fell short of what Scottish people wanted.

“Under these proposals, less than 30 percent of our taxes will be set in Scotland and less than 20 percent of welfare spending will be devolved to Scotland,” he said.

The proposals will be introduced as legislation in Parliament in January.

They could open a constitutional can of worms, boosting calls for other British regions, and even major cities, also to be given tax-raising powers.

Cameron also promised to introduce a contentious proposal for “English votes for English laws.”

It is intended to address a quirk of Britain’s political system that means Scottish lawmakers in the House of Commons can vote on policies that only affect England.