Theresa May will vow never to allow the UK to become "looser and weaker'' in a speech ahead of a meeting in Scotland with Nicola Sturgeon.
English Votes For English Laws Plan
David Cameron has launched the Conservatives' first English manifesto, with a promise of changes to ensure that English MPs have the final say on income tax rates in England.
And the Tory leader made another bid to persuade Ukip supporters to back his party in the General Election, with a warning that a Labour government backed by the Scottish National Party would result in "a return to uncontrolled immigration''.
Chancellor George Osborne marked the publication of the English manifesto by posing for photos in The Sun with a flag of St George in a pub in Ed Balls's Morley & Outwood constituency. He said he was "proud'' to fly the red-and-white flag, which had been "recaptured'' over recent years.
The English manifesto sets out a timetable for the implementation of Conservative plans for English votes for English laws in the House of Commons within a year of the May 7 election and a promise to extend it to financial issues, in reflection of the devolution of tax-raising powers to Scotland.
From the Budget expected in March, whenever taxes have been devolved to Scotland, Conservative plans would require the consent of English, Welsh and Northern Irish MPs to set the level in those parts of the United Kingdom.
A Conservative government would bring forward proposals within 100 days of the election for amendments to House of Commons rules to give an effective veto over England-only issues to English MPs. Where measures also apply to Wales or Northern Ireland - as with income tax - MPs from those nations will also be involved.
Launching the English manifesto, Mr Cameron is expected to say: "We do not support English nationalists, we do not want an English Parliament, we are the Conservative and Unionist Party through and through. This manifesto simply recognises that the democratic picture has got more complicated in the UK, so beyond our main manifesto, English voters deserve one document, clarifying in black and white what they can expect.
"Soon, the Scottish Parliament will be voting to set its own levels of income tax - and rightly so - but that has clear implications. English MPs will be unable to vote on the income tax paid by people in Aberdeen and Edinburgh while Scottish MPs are able to vote on the tax you pay in Birmingham or Canterbury or Leeds. It is simply unfair. And with English votes for English laws we will put it right.''
Turning his fire on Labour over immigration in an article for the Daily Mail, Mr Cameron said: "The only way Ed Miliband can get into Downing Street is if he is propped up by the SNP - and they have made clear that they want higher levels of immigration. It's clear: Ed Miliband in Downing Street would increase immigration, not reduce it.
"And if you're someone considering voting Ukip because you want a referendum on Europe and controlled immigration, remember that a vote for Ukip makes it harder for Conservatives to win - and much more likely for Ed Miliband and the SNP to get into government. Then you will get no referendum, and a return to uncontrolled immigration.''
A Labour spokesman responded: "The increasingly desperate Tory campaign resorts to lies once more - this time on immigration.
"The facts are that it is David Cameron who has broken his 'no ifs, no buts' promise to bring net migration down to the tens of thousands. Indeed net migration is now almost 300,00 - far higher than when he became Prime Minister.
"Labour has a better plan to control immigration by ensuring people can't claim benefits for at least two years, making it illegal to undercut local jobs and wages by exploiting workers coming here, and delivering 1,000 extra border and enforcement officers.''
Under English votes for English laws, the committee stage of the parliamentary process - during which bills are subjected to detailed line-by-line discussion - will be reserved for MPs from the nations affected by the legislation. No bill or part of a bill relating only to England could become law without being approved in a Grand Committee made up of all English MPs.
The Tories' English manifesto contains guarantees for England to continue with policies - such as rising NHS budgets, more freedoms for schools, the extension of right to buy to housing association tenants, a real-term freeze on rail fares and more free childcare for three and four year olds - even where they do not exist or are called into question elsewhere in the UK.
Mr Cameron will say: "My message to people who want these things, who want their own home, more childcare, an NHS protected and their taxes cut, is: there is only one way to guarantee it: Vote Conservative on May 7.''
Labour shadow communities secretary Hilary Benn said: "The truth about what the Tories are offering England is a plan for extreme cuts - double the cuts next year - which will put the NHS at risk.
"Only Labour has a better plan for working people: for living standards, the NHS and the next generation. It's also a plan which will see us pass an English Devolution Act and transfer £30 billion and new powers back to England's cities and counties to boost economic growth in every part of the country.''
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