"Increasingly desperate" Scottish nationalists will pull any trick they can when Holyrood returns to business for its unprecedented summer session after the Commonwealth Games, according to Better Together leader Alistair Darling.

The SNP voted to change Holyrood's recess dates to sit in August before the referendum 'purdah' period begins, giving the Scottish Government the opportunity to announce new policies and initiatives ahead of the period of silence.

About a quarter of Scots have registered for a postal vote - rising to a third in some areas - meaning they will be casting their votes from the end of August, Mr Darling said.

"That means that we have a short, critical time but we are increasingly confident about the arguments that we are making," he said at the opening of a Better Together campaign office in Paisley, Renfrewshire.

"It's manifestly obvious that the nationalists are running out of arguments and running out of time, which is why I suspect that after the Commonwealth Games you will see them become increasingly desperate in the things they say."

The Scottish Parliament returns to business on August 5. Scottish Deputy First Minister Nicola Sturgeon and the Local Government Minister, Derek McKay, opened a Yes Scotland shop in Paisley on Monday.

Ms Sturgeon said: "'Westminster knows best' is the very essence of the No camp's message but it is demonstrably untrue, and it has a rapidly diminishing appeal among Labour voters in Scotland.

"A Yes vote is the chance of a lifetime for Labour voters to reclaim their politics and their party - and put Scotland on a path towards the goals and ambitions they support.

"Instead of seeing up to 100,000 more children pushed into poverty because of Westminster austerity, we can get rid of Trident nuclear weapons and transform childcare to benefit 240,000 children. I have yet to meet a Labour voter yet who puts bombs before bairns."