THE SNP’s longest-serving MP has said his party should emulate Mel Gibson in Braveheart in deciding when to call a second independence referendum.

Pete Wishart said the SNP should wait to “strike at the optimum time”, just as William Wallace did before attacking the English cavalry at the Battle of Stirling Bridge in 1297.

Scottish Labour said the comment was extraordinarily embarrassing, even for Mr Wishart.

The Perth & North Perthshire MP, who is considering standing for the deputy leadership of the SNP, set out his approach to an another referendum in a column in The National.

Glasgow Cathcart MSP James Dornan, the only declared contender for the SNP deputy position, last week said another referendum could easily be held next year.

However Mr Wishart urged caution, saying the party should only go to the country when it was “certain of winning”, something which is technically impossible in a fair contest.

He said: “I know it is a crudely constructed piece of history more designed for Hollywood than Holyrood but I love Braveheart.

“My favourite part is when the Scots are assembled at Stirling Bridge itching to get into battle and William ‘Mel’ Wallace instructs them to ‘hold… hold… hold…’ before unleashing the weaponry that would lead to victory [long wooden spears in the 1995 film].

“Our approach to a second referendum has to be a bit like that and we must be patient and, like Mel, strike at the optimum time for success.”

Mr Wishart, who held off a Tory challenger to his seat by just 21 votes last year, said it would be “unthinkable” for Yes supporters to lose a second referendum, and it may well be best to delay another one until after the next Holyrood election in 2021.

He said: “If the optimum conditions are assessed to be found on the other side of a Scottish election then we should properly prepare and ensure that a mandate is once again forcefully renewed, undisputed and incontrovertible.”

Labour MSP Rhoda Grant said: “Pete Wishart is an MP known for his embarrassing interventions - but even for him this is extraordinary.

“The sum total of the SNP’s unwanted drive for independence now seems to be taking inspiration from Hollywood scripts.

“The people of Scotland would rightly hope that after the fiction of the SNP’s white paper on independence, Nationalist politicians might have learned their lesson and try sticking to fact.

“Rather than spending his time watching films from twenty years ago, Pete Wishart would do better to urge Holyrood colleagues to stop the SNP’s devastating cuts to lifeline services.”