A MASS gathering of SNP MPs and MSPs is to take place early next month as the party gears up to launch its long awaited summer independence initiative.

Senior sources have said that attendance at the event in Stirling is a must and such is its importance that a “three line whip” has been imposed on all 119 parliamentarians.

The meeting at the Golden Lion Hotel on Friday, September 2, has been scheduled for some months and was initially planned solely as an “away day” for Westminster, Holyrood and Brussels representatives to get to know each other and to co-ordinate working across the different parliaments.

But it is understood that parliamentarians are keen to discuss the shock Leave result of the European Union referendum in June, its implications on Scotland and on the prospect of a second independence referendum.

The summer independence initiative, initially planned for the holiday period, was delayed while the party took stock of the shifting political situation following the Brexit vote and last week the party said it would be unveiled before the end of the Holyrood recess on September 5.

Party leader and First Minister Nicola Sturgeon is currently examining options to see if there is any way of maintaining Scotland’s close relationship with the EU as part of a UK which has left the bloc in a bid to reflect the overwhelming Remain result north of the Border.

She has set up an advisory group on Scotland’s relationship with the EU, led by Professor Anton Muscatelli of Glasgow University, to consider possibilities for the way forward, however she has also said a second plebiscite on Scottish independence is “on the table” and “is highly likely”.

One MP said: “The Westminster and Scottish Parliament SNP groups are having an away day on September 2. There’s a three line whip to attend, it’s a must. I haven’t seen the agenda yet, but discussion about Scottish independence and a new campaign are very likely to come up.”

A second parliamentarian said: “I would be shocked if we didn’t discuss independence... Independence will always be at the forefront of what we do and of course we want to talk about ways of how we can make a Yes vote more likely.”

A third added: “The objective of the day is to co-ordinate the workings of the two parliamentary groups. Independence will be discussed though the situation is quite murky because of the Brexit situation.

“I’m sure we will be discussing the parameters of what might happen. But we need to know what the Brexit plan is and we need to know if Theresa May is serious about looking at ways of keeping Scotland in the UK and the EU.”

The mass meeting comes six weeks ahead of the SNP’s annual conference when independence will again take centre stage after it was controversially absent from the party’s agenda at its main conference last year.

A resolution published in the new draft agenda for the three-day event in Glasgow in October calls for the country to prepare for a second independence referendum if Scotland’s EU membership is not safeguarded once the UK exits the bloc.

It says: “Conference believes that every avenue must be explored to keep Scotland in the EU. If no viable solution to safeguard our membership as part of the UK exists, Scotland should prepare for a second independence referendum and seek to remain in Europe as an independent country.”

The resolution was put down by Toni Giugliano, of the SNP’s Edinburgh Western branch, and also welcomes the result that 62 per cent of voters in Scotland backed the Remain case, and expresses disappointment that the UK voted overall to Leave.

“Conference believes that it would be democratically unacceptable if Scotland were to be dragged out of Europe against its will.

“Conference expresses its disappointment that the UK as a whole voted to leave the EU but reaffirms that the democratic will of the people of Scotland must be respected,” it adds.