A LAW expert has raised concerns that Scottish Government proposals to hand powers currently held by the EU to ministers rather than MSPs after Brexit are not appropriate and cannot be justified.

Professor Aileen McHarg, professor of public law and human rights at Durham University, has also warned that the Scottish Government’s aims to keep pace with EU law could become “less useful in practice” as the UK Government’s internal market proposals will mean Holyrood’s proposals “will be overtaken by whatever happens in other parts of the UK”.

The expert was appearing in front of Holyrood’s Finance and Constitution Committee as MSPs considered the Scottish Government’s EU Continuity Bill.

Part of the bill would hand Scottish ministers the power to continue to keep devolved law aligned with EU law once the Brexit transition period ends on 31 December. Professor McHarg told MSPs that “we must question whether a ministerial power is the appropriate way to go at all”.

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She said: “I don’t see in that case, there are any justifications really of pressure of time – directives have a very long lead-in time, they usually have a lengthy time for member states to come into compliance. “I think it’s hard to see why those kind of policy choices should be seeded to the government rather than retained by the parliament.”

She added: “My preference would be for primary legislation because ministerial powers of this nature ought to be seen as exceptional and as requiring some special justification.

“It seems very hard to me to justify a power as extensive as this one in the hands of ministers.”

The UK Government has drawn up a white paper to act as a blueprint for trade after the Brexit transition period ends on December 31 – labeled the UK internal market.

Scottish Constitution Secretary Mike Russell has branded the measures the "biggest threat to devolution since the Scottish Parliament was reconvened in 1999", and has indicated the Scottish Government will "actively oppose the UK Government's proposals at every opportunity".

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UK ministers have said it will result in 111 powers being transferred to Holyrood from Brussels.

Professor McHarg said that UK Government plans will likely cause “significant constraints”.

She added: “The internal market proposals , if they are implemented in the form that appears in the white paper, won’t technically prevent the use of the keeping pace power, but what they will do is probably render it less useful in practice because the effect of Scottish divergence will be overtaken by whatever happens in other parts of the UK.

“It’s just very, very difficult to know at the moment what’s going to happen because there’s still so much uncertainty.”

Professor Michael Keating from Aberdeen University told MSPs that the internal market plans are “really problematic” and offer a “risk of confusion”.

He added: “If we have rather ill-defined internal market provisions that allow the UK to intervene, prescribing mutual recognition that undermines Scottish regulation, if we have trade deals, if we have frameworks - it could create a great deal of uncertainty rather than more certainty for stakeholders.”

Greens co-leader, Patrick Harvie, pressed the experts over the UK internal market plans.

He said: “From my perspective, it looks at though they are incompatible, it looks as if the purpose of the Scottish Government is to keep pace and the purpose of the UK Government is to diverge from Europe, to undercut Europe on standards and to impose those lower standards on Scotland – either through trade agreements with other countries or through giving the private sector the right to challenge regulations of the internal market proposals.

“Is there a way in which these two bits of apparently conflicting agendas can be made to work together?”

Professor McHarg warned that “we just don’t know how much divergence there will be in future”.

She added: “What is clear is that if trade agreements require a divergence from EU standards, those trade agreements can be made binding on the Scottish Parliament even if they effect devolved areas.

“The internal market provisions are more nuanced than that in that they don’t deprive the Scottish Parliament and Scottish Government of the power to diverge – but they will tend to undercut it in practice because in practice the standards that are applied in the largest part of the internal market in the largest part of the internal market, i.e. England, goods and services complying with those standards will be able to be sold in the other parts of the UK. That’s a question of practical effect rather than being undermined in principle.

“What the concern is, is the area of discretion is being whittled away very, very significantly. The idea in principle that they might be convergence in some areas and divergence in other areas, that’s devolution. We’re talking about where the balance between those things lies.”

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SNP MSP Angela Constance stressed that the Scottish Government has “very legitimate political interests and considerations”.

She added: “The evidence that committee has received thus far and what we have heard this morning, I think very helpfully separated out some strands.

“On the one hand, we have really important technical considerations around process and scrutiny. On the other hand, we have the political motivations and considerations which I would content are very important around Scotland’s future relationship with the EU, our economy, the UK Government trodden over the devolution settlement and what amounts to a power grab.

“From my perspective, I don’t want my government to be sitting back and just accepting that they are going to be overruled at every twist and turn.”

But Tory MSP Dean Lockhart asked the experts “is this bill actually necessary at all?”

Professor McHarg said that in relation to keeping pace with EU laws, “it may become necessary but that depends on what the future relationship is with the EU”.

She added: “At the moment, I would say that it is not necessary – it's a choice. It is a legitimate choice for the Scottish Government to make – it wants to keep pace with EU law, that’s a reasonable thing for a government to do.