AMENDING the law to allow constituents to recall defecting MPs would be an “appropriate” and “legitimate” democratic change, a legal expert has said.

MP Dr Lisa Cameron defected from the SNP to the Conservative Party on Thursday, claiming she made the decision due to a “toxic” working culture in her former party’s Westminster group.

The move means the SNP now have just 43 representatives in the House of Commons, despite voters electing 44 in the 2019 general election – with the Tories’ total number growing to seven.

The decision came just hours before she was likely to be deselected as an SNP candidate at the next General Election.

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Keith Ewing, who is a professor of public law at King’s College London, has said that it would be “worth pursuing” amendments to the 2015 Recall of MPs Act which would add MPs defecting to a different party to the list of reasons and allowing their constituents to sign a recall petition.

If such a petition receives signatures from 10% of the local electorate, a by-election is immediately triggered in the constituency.

Ewing said the fact MPs are still freely allowed to “cross the floor” is an example of how “modern practice has failed to keep pace with changing democratic expectations”.

He said: “When I elect my MP I don’t expect that individual to go off on a frolic of their own, I expect them to support the party they stood for.

“It is a betrayal of the trust of the electorate for the member to be elected and then to defect.”

He said that the UK electoral system is still based on the views of the 18th-century MP Edmund Burke, who gave an influential “speech to the electors of Bristol” in 1774 which set out his responsibility to be an individual representative of his constituents. This goes in contrast to the “delegate” political theory in which an MP is seen as accountable to their party as well as their constituents.

He added: “It’s a hangover from a pre-democratic era which probably is not that appropriate for a constitution which now accommodates a system of very strict parliamentary discipline.”

Ewing, who is from Dunfermline but now lives in Cambridge, echoed First Minister Humza Yousaf, who said on Thursday that Dr Cameron should “do the honourable thing and step down”.

He added: “If somebody does defect and chooses to continue in office as an MP then I think there should be a case for saying there should be the possibility of a recall petition.

“Electors should be free to require a by-election if sufficient numbers so choose.”

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He added: “It’s close to an election now as well. It’s not as if this was the first year of Parliament, so in this case, the problem is probably not as acute as it would be if [Cameron] had defected three years earlier. But it’s nevertheless irritating.”

Dr Cameron is not the only MP to defect from the SNP in recent years, with both Kenny MacAskill and Neale Hanvey leaving to join former first minister Alex Salmond's Alba Party.

Dr Caroline Morris, reader in public law at Queen Mary, University of London, said that while introducing changes to the 2015 Recall of MPs Act would be the best legal route to holding politicians accountable for defecting,  it would risk breaching human rights rules.

She said: “You could add ‘the MP has left the party of origin’ as a ground for a recall petition.

“And say that by defecting the MP has flouted the terms of the delegation, if you like.

“If you put that in [law] and there was a petition, I think there would immediately be a Human Rights Act claim (HRA) saying that this provision in the Recall of MPs Act contravenes the individual MP’s right to freedom of speech and freedom of association – it’s not a proportionate response.

“Looking at how courts across the world have answered that question, I think the legislation would be found to be in breach of the HRA."

She added: “I tend to the view that political problems are best solved by politics rather than law.

“What you tend to see is that MPs who defect from their party of origin, in the main, tend not to get re-elected. Unless that MP is an absolute stellar stand-out with a big personal following, they’re generally not enough to transcend party loyalties."

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Dr Morris said that other countries have introduced defection laws in the past, but often for different reasons such as to prevent corruption and to ensure stability of government.

Some countries, such as New Zealand and South Africa, have had various defection laws but have since abandoned them.

She added: “Lots of countries have legislated against MPs defecting or crossing the floor in some way, but the legislation tends to not be very effective, either practically – because the costs of defying it are worth it – or because you end up in legal trouble for contravening the MPs' human rights."

A recall petition has only been used once previously in Scotland after MP Margaret Ferrier was found to have breached Covid rules, triggering the recent Rutherglen and Hamilton West by-election which saw Labour MP Michael Shanks elected.