Sir Keir Starmer will tomorrow set out plans to "preserve the United Kingdom" by promising greater devolution - after 17 polls have found most Scots now back independence.

The Labour leader is to promise a new package of powers for Scotland, as well as for the English regions, as he rejects calls for a second independence referendum.

Starmer who has previously refused to rule out the possibility of supporting a second referendum on the future of the union, is expected to say that he doesn’t “believe in putting up borders across any part of our United Kingdom”.

He will argue that "the richness of the UK" is measured not only in power or prosperity but by shared “history, values and identity” that has made borders obsolete.

But his plans - which come 11 days before the UK leaves the EU transition period without yet knowing on what terms - have been condemned by the SNP.

They also come after the latest poll, published last week, put support for independence at a joint record of 58% and the SNP on course to win a majority at next year's Holyrood elections.

Previous polls have also suggested that around 40% of Labour voters back independence and in recent weeks one senior former Labour aide has also said he now backs independence.

Duncan Maclennan, one of Donald Dewar's key advisers and now professor of public policy at Glasgow University, said that he no longer believed federalism would happen. 

Responding to the Labour leader, Kirsten Oswald MP, the party's Westminster deputy leader, said: "The reality is that the Westminster system is broken and not working for Scotland - and no amount of constitutional tinkering of the kind proposed by Labour will protect Scotland from Brexit or the Tory power grab being imposed upon us against our will.

"With a recent survey of Labour members revealing that a majority of UK and Scottish members don’t think Labour can oust the Tories for another decade at least, and a former special advisor to three Labour Scottish First Ministers stating that the 'best first constitutional move...is to seek Scottish independence," people in Scotland will not be fooled by Labour's empty constitutional claims.

"It's clear that only with the full powers of independence will we be able to properly protect our interests and secure our place in Europe - and that decision lies solely with the people of Scotland, not an out-of-touch Westminster system."

Starmer is to promise a new era of devolution, and will pledge that the next Labour manifesto will “aim to win power, in order to push as much power as possible away from Westminster”.

In a major intervention which will set the tone for UK Labour and Scottish Labour’s campaign for next year’s Holyrood elections, Starmer’s speech will set out how the next phase of devolution can build a more democratic and socially just Scotland in a modern United Kingdom.

Promising “a positive alternative to the Scottish people”, the Labour leader will recognise the need to build on Labour’s long tradition of promoting and implementing devolution as a vehicle for social justice.

It follows a series of opinion polls indicated that a majority of voters in Scotland now favour Scottish independence.

Speaking about his commitment to the Union, Starmer is expected to say: “Our nations are bound by our history, values and our identity. Our families live across borders and our businesses operate across borders. We’re interconnected and we’re interdependent.

“That’s not just a precious inheritance or a description of the past, it’s what we are. It’s what I want for our children, for the next generation.”

Scottish Labour was last week plunged into further turmoil when its top official and director of communications resigned five months before the Holyrood elections.

Michael Sharpe, a close ally of leader Richard Leonard, and Lynn McMath, announced they were both leaving their posts.

Their departures were blows to Leonard as his party struggles for relevance after a string of electoral losses, and is financially dependent on the UK Labour Party to keep it afloat.

Opinion polls have also suggested further losses for Labour at next year's Holyrood election with one survey published last week suggesting it would lose five MSPs going from 24 to 19, on just 16% of the vote.