Unionist supporters gather near George Square in Glasgow on Wednesday. Getty Images/Jeff J Mitchell

EDINBURGH—Now Scotland won't be leaving the U.K., the real work begins.

Prime Minister David Cameron and senior politicians from the U.K.'s main political parties have pledged to transfer more tax and spending powers to Scotland's semiautonomous parliament in Edinburgh from Westminster, where the U.K. government sits. But there are major hurdles.

Chief among these is that the three political parties at Westminster don't yet agree on which powers to devolve to Edinburgh. Mr. Cameron's Conservatives, Ed Miliband's opposition Labour Party and Nick Clegg's Liberal Democrats, the smaller party in Mr. Cameron's governing coalition, have published competing visions for Scottish "home rule" over the past year. The differences could add as much as billions of pounds a year in revenue and substantially more autonomy.

Discussions are to begin immediately over which powers should be devolved, with political parties of all stripes to be invited to participate. According to a timetable set out during the referendum campaign by former Prime Minister Gordon Brown and endorsed by party leaders, parliament will publish a document in October setting out the whole range of possible powers that could be devolved.

There will then be a public consultation, and a preliminary piece of legislation is due to be published in November. A formal bill will be presented to parliament in January for debate and approval to give the changes legal force, according to the timetable.

Currently, Scotland receives a chunk of money from Westminster every year and can decide what to do with most of it—Edinburgh can direct 60% of its budget, including in key areas such as health and education. But it has extremely limited powers to raise revenue, through either taxes or borrowing. Nearly all taxes—including income tax, corporate tax and VAT, a sales tax–are collected nationwide and paid into the treasury's coffers in London. The revenue raised is then divided up and doled out to different regions.

The offer of greater transfer of powers has fueled accusations from nationalists that the unionists campaigning under the banner Better Together in their panic offered what was initially termed "devo max"—a deal whereby Scotland would remain in the U.K. but with additional powers that the Westminster parties refused to include as a third option in the referendum.

The day before Thursday's referendum, the government department that handles Scottish issues said that the exact mechanics of what would happen on Friday once a "No" is confirmed remain to be completed between the U.K. government, political parties, and their advisers. Mr. Cameron's office also said plans weren't set.

The Westminster political leaders have outlined a four-stage process, starting with cross-party talks on which further powers to devolve. In October, the parties will publish a parliamentary document setting out a range of possible tools and responsibilities that could be devolved. A public consultation on the proposals will follow ahead of the publication of preliminary legislation in November, and a formal bill will be put before parliament in January.

The offer of further devolution for Scotland could prompt other regions in the U.K. to push for greater powers. Matthew Flinders, a politics professor at the University of Sheffield, said Scotland's decision to stay in the U.K. could lead to demands from other U.K. regions, such as Wales, parts of England and to some extent Northern Ireland, that will also want more autonomy from the U.K. Parliament in London.

And, Mr. Cameron now must turn his focus to another major fight. He has pledged to hold a referendum in 2017 on whether the U.K. should exit the European Union should he win the U.K. general election in May.

Write to Jason Douglas at jason.douglas@wsj.com and Jenny Gross at jenny.gross@wsj.com