Boris Johnson has said Jeremy Corbyn and Nicola Sturgeon are yoked together to destroy the Union as he pledged to block a second Scottish independence referendum even if the separatists win a majority in the next Holyrood election.

Speaking on a visit in Moray, during his first full day of campaigning in the general election, the Prime Minister gave a "cast-iron" promise not to give Ms Sturgeon the powers for another separation vote.

Mr Johnson has previously said he would block another referendum if the SNP again wins a majority of Scottish seats in next month's election, but he went much further by extending his pledge to the 2021 Scottish Parliament contest.

He issued a scathing dismissal of Labour's denial that Mr Corbyn has reached a "shady deal" with Ms Sturgeon, granting her another vote in return for SNP MPs putting the Labour leader in 10 Downing Street, saying: "Pull the other one."

Asked whether he considered Mr Corbyn or Ms Sturgeon a larger threat to the Union, he said: "They are yoke-mates of destruction." The Prime Minister also used his visit to the Roseisle distillery to announce a review of spirit duty, the top demand of the Scotch whisky industry, in the wake of Donald Trump's decision to impose tariffs.