THE Tories have peaked in Scotland and will slip back into position as the third party at Holyrood, the SNP's chairman has said.

Derek Mackay said the claim, based on opinion poll findings, showed Ruth Davidson's party was losing support.

The attack came on the opening day of the Tory conference in Manchester today

Davidson has been given star billing at the conference in Manchester today.

The Scottish Tories increased their MPs from one to 13 in the General Election on June 8.

Davidson's party also replaced Labour as the second biggest group at Holyrood at the 2016 Scottish Parliament elections.

However, Mackay said Davidson's chances of ever being First Minister are increasingly remote.

Mackay highlighted a series of polls and by-election results he said showed Tory support was slipping in Scotland.

He cited a Survation poll taken last month that showed the SNP were backed by 31.2 per cent of those surveyed for regional list voting intentions in Holyrood elections.

The level of Labour support in that poll was 25.1 per cent and 21.1 per cent for the Tories.

Mackay also highlighted Survation polling for Westminster voting intentions in August that put the SNP on 39.3 per cent, the Tories on 26.1 per cent and Labour on 26.4 per cent.

A council by-election in Tain and Easter Ross last week also saw the Tory vote fell by 6.9 per cent since May’s council elections.

Mackay, who is also Scotland's finance secretary, said: "It is hugely encouraging that after ten years in government the SNP is recording double-digit poll leads, and we intend to continue working tirelessly to implement our most ambitious and greenest programme for government yet.

“All the while Ruth Davidson’s hubris and hype is overshadowed by the fact the polls show her party slipping behind the warring Labour party to third place in Scotland.

“The Tories are completely void of any ideas or serious policies and it’s catching up with them. Every week Ruth Davidson demands more spending yet lower taxes for the rich at the same time, they look more and more ridiculous and economically incompetent.

"The bottom line is that the Tories are just as toxic as ever in Scotland. They think they can do what they like to Scotland and get away with it."

Scottish Labour leadership contender Richard Leonard added: "Ruth Davidson's MPs and MSPs like to present themselves as the acceptable face of Conservativism but in fact they are part of the problem - failing to stand up for the majority in Scotland who want better-funded public services, an end to a brutal benefits regime, decent jobs and better pay."

The Sunday Herald approached the Tories for a comment about Mackay's claims but they failed to respond.