The UK will not be able to return to a 1970s-style "hoarding of powers" in London after Brexit, according to the author of the UK's most read textbook on public law.

In a major intervention, Professor Mark Elliott of Cambridge University has condemned any Conservative justification for retaining EU powers in key devolved areas such as fishing and farming as "specious".

The expert was speaking after the Scottish Government accused its UK counterparts of a "power grab" as they announced they would, at least initially, repatriate all responsibilities exercised by Brussels to Westminster.

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Prof Elliott confirmed that Theresa May's British government had all the sovereign legal might it needed to do this. But he added: "The UK Parliament’s legal sovereignty does not render it a monopolist when it comes to determining the acceptable rules of interaction between the several governments and legislatures that wield democratic power within a British constitution that is unrecognisable from that which existed when the UK joined the EU over 40 years ago.

"And in whatever other senses (positive or negative) leaving the EU may involve a turning back of the clock, it will not afford the UK Government the luxury of a 1970s-style British constitution in which power was hoarded in London."

In last year's Herald Beyond Brexit series experts warned that rhetoric of insuring a UK single or common market - akin to the EU one - would mean Holyrood's control of key areas could be peeled back.

The UK Govermnent has said some powers - after being repatriated to Westminster - would be “released” to Holyrood and the other devolved administrations, with others subject to UK-wide “common frameworks” to avoid disrupting the UK’s internal market.

The SNP says the Bill is a “power grab” and a threat to the entire devolution settlement, as it would mean Westminster taking control of powers in devolved areas.

Prof Elliot explained that the UK's repatriation law would, effectively, amend the devolution settlement. It has the power to do this - but such a move, he argued had a substantial political risk of over-riding notions of pooled sovereignty developed in Northern Ireland, Scotland and Wales over the last two decades.

Writing on his website, he said: "There are fundamental difficulties with attempting to play that sort of trump card in order to override the kind of concerns being raised by the Scottish Government.

"For one thing, leaving the EU was not the will of the Scottish people. And, for another, the referendum result — notwithstanding some politicians’ inclination to treat it as a blank canvas upon which politically expedient positions can be painted with abandon — surely cannot be taken to provide any cover, either way, in relation to the question of whether repatriated EU powers go to the devolved capitals or only to London."