Theresa May could struggle to negotiate a Brexit deal that will win the backing of the House Commons - which could see the country forced into a general election at the end of next year, the author of Article 50 has warned.
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Former diplomat Lord Kerr of Kinlochard also said the UK Government would have to amend key parts of its Brexit legislation because the European Union (Withdrawal) Bill seems to "fly in the face of the devolution settlement".
Both the Scottish and Welsh governments claim the Bill as its stands is a Westminster "power grab", and have put forward amendments they say must be passed if they are to back the process.
Lord Kerr said the "fundamentally important" concept that all powers are devolved apart from those specified in legislation as being reserved to Westminster "has for the first time been broken in my view".
The former ambassador, who was UK Permanent Representative to the European Communities/European Union in Brussels from 1990 until 1995, spoke out as he gave evidence to MSPs on Holyrood's Europe Committee.
He told members that "there will have to be changes made" to the Withdrawal Bill as it goes through the House of Commons this autumn and the Lords in spring 2018.
He added: "Next autumn's drama, autumn 2018, is the deal or no deal. And I cannot now see any negotiable deal for which there is a majority in the House of Commons.
"It seems to me there are sufficient hardline Brexiteers to make it very difficult for the Prime Minister to compromise sufficiently to get a deal in Brussels and if she does these people might vote down her deal."
Lord Kerr continued: "I can see a situation in November/December when the outlines of the deal or no deal are becoming clear - November/December next year - and there will be a requirement for a parliamentary vote, even if it is no deal.
"At that stage I think we could be quite close to an election."
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