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Theresa May is to tell the two men vying to replace her as prime minister that they must make strengthening the union one of their top priorities.

In a speech in Scotland on Thursday, Mrs May will urge her successor to "think creatively" about how to ensure the UK stays together.

She will also give further details of a review into how devolution is working.

The review is aimed at ensuring UK government departments are working in the best interests of devolution.

The government has stressed it will not include devolved areas that are the responsibility of the Scottish government.

Scotland's first minister, Nicola Sturgeon, predicted ahead of the prime minister's speech that the review was "too little, too late" and would do nothing to prevent Scottish independence.

Mrs May's speech is likely to be her last in Scotland before she steps down as prime minister on 24 July, when she will be succeeded by either Boris Johnson or Jeremy Hunt - who are both due to appear at a hustings event in Scotland on Friday.

Mr Johnson said on Sunday that the next prime minister should be a "minister for the union" while Mr Hunt has pledged to to use "every drop of blood in my veins" to prevent the UK splitting up.

But Ms Sturgeon, who wants another referendum within the next two years, has already predicted that more Scots will be encouraged to support independence regardless of who wins.

In her speech, Mrs May will insist that strengthening the union has been an "explicit priority" of her government over the past three years.

And she will say she is confident that this will continue to be the case regardless of who replaces her in 10 Downing Street.

Mrs May will add: "The job of prime minister of the United Kingdom of Great Britain and Northern Ireland brings with it privileges and responsibilities which you only really feel once the black door closes behind you.

"One of the first and greatest is the duty you owe to strengthen the union. To govern on behalf of the whole United Kingdom. To respect the identities of every citizen of the UK - English and Scottish, Welsh and Northern Irish.

"And to ensure that we can go on facing the future together, overcoming obstacles together, and achieving more together than we ever could apart - a union of nations and people."

Mrs May will also formally unveil a UK government review of how devolution is working across the UK and what can be done to improve it.

Scotland Office minister Lord Duncan told the BBC on Wednesday that it would be a "simple, straightforward way of making sure devolution is working as best as it can be".

Ahead of the prime minister's arrival in Scotland, Ms Sturgeon claimed that the country was "heading inexorably towards independence" and that the Conservatives were "running scared of the rising tide of support for independence".

She added: "The Tories' behaviour towards Scotland in the three years since the Brexit vote has been high-handed, arrogant and dismissive.

"They have demolished any notion of a respect agenda and have destroyed their own claims that the union is in any meaningful way a partnership of equals.

"People across Scotland can now see that more plainly than ever. Theresa May's so-called review of devolution is too little, too late".