TORY squabbling over Brexit is placing jobs and incomes in "grave peril", Scotland's Europe minister has said.

Mike Russell issued the warning after Ruth Davidson and Boris Johnson bitterly clashed ahead of the Tory conference.

Russell said the party's civil war over Europe would destroy the prospect of a smooth Brexit transition deal.

The SNP minister said the internecine Tory warfare was causing growing economic uncertainty.

He said Tory Brexit plans were in "disarray" after "this latest bout of infighting" between Davidson and Johnson.

Boris Johnson insisted that any post-withdrawal transition period must not last "a second more" than two years.

However, Scottish Tory leader Davidson called for "serious people" to take charge of Brexit in a thinly veiled attack on the foreign secretary.

Davidson is to address the Tory conference in Manchester today, when she is expected to be given star billing.

Davidson warned that "over-optimism" about the future of Britain outside the EU "sells people short".

Johnson set out four "four red lines" for Theresa May over Europe in a dramatic intervention on the eve of the Tory conference.

Using increasingly hyberbolic language, Johnson said that Brexit will be "great" and "unstoppable".

The foreign secretary set out four conditions he says are necessary for leaving the EU.

Johnson insisted any transition period after Britain leaves the EU should not last more than two years.

He insisted the UK must refuse to accept new EU rules during that period.

Johnson also said there must be no payments for access to the single market after the end of the transition period.

He added that the UK must not agree to shadow EU rules to gain access to the trading bloc.

However, Russell, Scotland’s Minister for UK negotiations on Europe, said the Tory Government's "lack of clarity" on Brexit was damaging business confidence.

Russell warned this was placing jobs and incomes at risk.

He said: “The Tories are clearly in disarray which means that Brexit is in disarray and it is difficult to see where they go from here.

"This latest bout of Tory squabbling on Brexit demonstrates two things. First, they still do not know what they want from Brexit and now we have the UK’s Foreign Secretary wanting something as a red line which is simply impossible to achieve. Indeed, his conditions would in effect scupper the prospect of any transition.

"Secondly, if they carry on like this, no one will trust them. EU member states cannot be expected to take them seriously in the negotiations when every week a new position emerges and a new spat is ignited.

"The continued uncertainty and lack of clarity on the terms and potential impact of Brexit is damaging confidence in our economic prospects - and it puts all that matters to Scotland, including people’s jobs, businesses and incomes, in grave peril.”

Johnson said that Brexit is "going to be great and we need to believe in ourselves and believe we can do it".

The foreign secretary added: "It is unstoppable."

Johnson's intervention will fuel speculation of a challenge to Theresa May who will be seeking to reassert her authority as she goes into her first party conference since she lost her government's majority in the General Election.

However, Davidson took aim at those setting out what she sees as an unrealistic prospectus.

In an eve of conference interview, she said: “I think optimism, positivity is good. I think over-optimism and not recognising that there are practical realities that have to be faced, that have to be worked through and that complexity is not something you just skip over, that you actually have to work through, I think sells people short.”

Davidson denied that the comment was directed at Johnson.

However, when asked about Johnson’s upbeat message, Davidson said: "I don't take issue with optimism. I am quite often accused of having a kind-of, sort-of have-a-go element about myself as well.

"But there is the idea that this is quite hard and it needs serious people to do a lot of legwork and scan the detail to make sure we do get to a place where it will all be OK.

"It doesn't just happen by accident, it requires a lot of hard work and it requires application."

Meanwhile, Labour's shadow Brexit secretary Keir Starmer has challenged Scotland's 13 Tory MPs to back his amendments to key Brexit legislation and help protect devolution.