The Prime Minister will launch the Scottish "vote yes" campaign in the foreword to the Scottish devolution White Paper to be published on Thursday, in which he promises a "new Scotland in a new Britain".
The White Paper will make it clear that sovereignty will stay with the Westminster Parliament, reinforcing the Government's denials that it will lead to the break-up of the Union.
The Government has decided that there will be no bar on the Scottish Parliament debating and voting for independence, but it does not expect this to happen.
The decision not to put a "glass ceiling" on the debates of the Scottish Parliament is expected to be enough to win the backing of the Scottish Nationalist Party for the "vote yes" campaign. However, the Government and leaders of the SNP yesterday strongly denied any deal-making.
Ron Davies, the Secretary of State for Wales, said that this power would not be given to a Welsh Assembly. The devolution White Paper for Wales will be published tomorrow, accompanied by campaigning in favour of a "yes" vote. Mr Davies said on BBC Breakfast with Frost that he had opposed devolution in 1979 but that circumstances had now changed.
"There is now a need to ensure that the power devolved to Cardiff and discharged by the Secretary of State is subject to a more direct control by the people of Wales through their own representatives," he said.
The "Wales says yes" campaign will be launched tomorrow with a celebrity reception at Cardiff Castle hosted by Sian Lloyd, the ITV weather presenter, with Ryan Giggs, the Manchester United star, Colin Jackson, the Olympic hurdler, and the band Manic Street Preachers.
The "Just Say No" campaign is to be launched today in Wales and will be reinforced tomorrow by William Hague, the Conservative Party leader and former Secretary of State for Wales, as he opens his campaign against devolution at the Royal Welsh Show.
The Scots are expected to vote overwhelmingly in favour of devolution in the Scottish referendum on 11 September, but the Government is anxious to ensure a "yes" vote in Wales on 18 September. Private Labour focus group sampling suggested that having the Welsh referendum after the Scottish vote "yes" could add 10 per cent to those in Wales voting for the new parliament.
The White Paper for Wales will propose: A 40 member assembly, to be elected every four years by first past the post, with 20 more from the five European Parliament seats in Wales; it will have no tax-raising powers but it will have responsibility for the pounds 7bn Welsh grant; the Assembly will elect a leader, with a 10-member executive, but the Secretary of State for Wales will remain in the Cabinet in London.
The White Paper for Scotland will propose: a 129-member Parliament, elected by first-past-the post and additional member system; it will have tax- varying powers and the right to pass primary legislation, and autonomy over spending for most services. There will be a Chief Minister, elected by the Assembly, with a Cabinet, but the Secretary of State for Scotland will remain in the London cabinet.