The leader of the UK's largest union has backed left-wing MSP Richard Leonard to be the new leader of Scottish Labour - and said his leadership could help Labour back to power across the UK.

Len McCluskey, the general secretary of the Unite trade union, said if Mr Leonard was voted in to succeed Kezia Dugdale, Labour north of the border would "build on the foundation laid by Jeremy Corbyn".

Mr Leonard is competing for the job against the more moderate MSP Anas Sarwar, who is Labour's Holyrood health spokesman, with voting in the contest now under way.

Speaking as he addressed the Unite Scottish policy conference in Aviemore, Mr McCluksey said: "Scottish Labour needs a leader who speaks for workers. We have one in Richard Leonard."

He said that this time last year "Labour in Scotland had fallen off the electoral perch" but said the party's success in the June general election, winning seats back from the SNP to return seven MPs to Westminster, had helped turn things round

Mr McCluskey stressed there was still "a lot to do to rebuild from the 2015 wipeout" when Scottish Labour lost 40 MPs to Nicola Sturgeon's party

But he added: "Who would have thought, even a few months ago, that we would be talking about Labour's fortunes in Scotland being the key to open the door to Labour in No 10."

Mr McCluskey claimed that while voters were fed up with the "weary same old politics", politicians such as Mr Corbyn and Mr Leonard had "something genuinely new on offer".

The Unite boss said: "Just as people warm to the honesty and decency of Jeremy Corbyn, voters in Scotland can look at Richard Leonard and say 'he's on my side'."

A spokesman for the Anas Sarwar campaign said: "We know that many ordinary members of Unite and other trade unions are backing us because we're running a positive campaign focused on radical ideas.

"Anas is standing in this contest as the only candidate who has never, and will never, leave workers behind by voting against the Labour Party and with the Tories on Brexit.

"Nobody can credibly claim they want to protect jobs and not support membership of the single market and the customs union. That's why Anas supports permanent UK membership of the European single market and the customs union."