Holyrood ministers are unlikely to be treated as equal partners by Westminster in Brexit talks, MSPs have been told.

Akash Paun, a fellow at the Institute for Government think tank, said while he expects more than just "consultation at the margins" between the UK and the devolved administrations, it is not likely there will be "four equal partners round the table".

Speaking to the European and external relations committee on Thursday, Mr Paun added Brexit would "probably" trigger a constitutional crisis if it was forced through without agreement from Holyrood.

He also said the Scotland Act "will need to be revisited" in light of Brexit and the process of Britain's exit from the EU will open a "box of issues" the UK Government is yet to fully grasp.

Discussions have been taking place over the roles of ministers in Edinburgh, Cardiff and Belfast when the UK begins to negotiate its exit from the EU.

An initial meeting took place between Holyrood's Brexit minister Mike Russell and his UK counterpart David Davis last week.

Mr Paun said EU membership "cuts across the devolution settlements in such complex ways that we do need to think about this as a UK-wide decision".

He added this "isn't the same as saying there is going to be four equal partners round the table - I don't think that's likely".

The reality, Mr Paun said, would likely be "somewhere in between" full partnership and "how things have too often worked in practice, where it is treated as a pure Westminster competence with consultation at the margins with the devolved governments".

Committee convener Joan McAlpine asked Mr Paun if he believed a constitutional crisis would be triggered if the UK pushed ahead with negotiating its exit from the EU without agreeing on terms with the Scottish Government, to which he replied: "Probably, yes."

He told the committee: "At the end of the process, when some sort of Brexit deal is implemented, at that point I would very much expect we would see legislative consent motions put before probably all the three devolved legislatures, because Brexit will cut across devolved areas and will change the competencies, pretty much inevitably, of the devolved institutions.

"But the convention, even though it is recognised in Scotland Act 2016, is done so in a way that means it's probably not judicially enforceable, so I don't think that gives the Scottish Parliament a veto over Brexit.

"I think it would be in breach of established convention for the UK Government to push ahead with something that changed the constitutional settlement of Scotland radically without reaching agreement on the terms of that with the Scottish Government and Parliament."

The likelihood that Brexit would lead to the Scotland Act changing again was high, he said.

Mr Paun said: "We may come out of this with a very different set of constitutional arrangements both for governing the distribution of powers between different governments and also in areas where the UK takes back competence from Brussels.

"We may need new arrangements for coordinating policy between the levels of government as well.

"I think the UK Government certainly hasn't quite realised the whole box of issues that this opens up.

"I think it's pretty much inevitable that the design of the constitutional settlement and the Scotland Act will need to be revisited as part of this process."