Boundary changes which would result in Scotland losing six of its 59 seats at Westminster have been branded "unacceptable" by the SNP and Labour.

SNP depute leader Angus Robertson said the proposals were "outrageous and undemocratic" when compared to the House of Lords, which has grown to more than 800 members.

Labour's sole Scottish MP Ian Murray called the changes "unfair" and said they were "based on an out-of-date version of the electoral register".

The proposals, published on Thursday by the Boundary Commission for Scotland, will now be subject to consultation.

They are part of far-reaching plans to reduce the total number of seats in the House of Commons from 650 to 600 by the 2020 general election.

The UK Government say the changes will cut the costs of parliament and make constituencies more equal in size.

Robertson said: "The proposals to cut the number of elected representatives in Scotland are unacceptable.

"At a time when Scotland already faces a deep and growing democratic deficit, with a Tory government that we didn't vote for imposing increasingly right-wing policies against our will, it is vital that the Scottish people have strong elected representation at Westminster to stand up for Scotland's interests and to hold the UK Government to account.

"Furthermore, it is outrageous and undemocratic that the UK Government is planning to cut the number of Scottish MPs while it continues to pack the unelected and unaccountable House of Lords with yet more Tory donors and cronies to do the government's bidding."

Robertson's seat of Moray is to be expanded into a new Moray and Nairn constituency.

MPs in Glasgow, Dundee and Edinburgh will also be affected, with constituencies either being beefed up or absorbed into others, such as Murray's Edinburgh South seat.

Responding to the proposals, the Labour MP said: "Tory proposals to redraw constituency boundaries are unfair, undemocratic and unacceptable.

"They are based on an out-of-date version of the electoral register with nearly two million voters across the UK missing.

"While the Tories say this is to reduce the cost of politics, they are cutting directly elected representatives and stuffing the House of Lords with their own supporters."

Murray added: "In the past, ministers have argued that cutting the number of MPs will save the taxpayer £12m but David Cameron created scores of extra unelected peers in the House of Lords, costing £34m.

"Labour has proposed abolishing the House of Lords, replacing it with an elected Senate of the nations and regions."

The recommendations only leave three seats north of the border unchanged - East Lothian and the island constituencies of Orkney and Shetland and Na h-Eileanan an Iar (the Western Isles).

In Glasgow, SNP education spokeswoman Carol Monaghan's Glasgow North West seat would be merged with colleague Patrick Grady's Glasgow North seat as the number of constituencies in the city drops from seven to six.

Former SNP MP Natalie McGarry, who now serves as an independent and was last month charged in connection with alleged fraud offences, will have her Glasgow East seat expanded.

Stewart Hosie, who resigned as SNP depute leader earlier this year, will have his Dundee East seat substantially absorbed into a new Angus Glens & Dundee East constituency, where he may have to compete with colleagues Chris Law (Dundee West) and Mike Weir (Angus).

With the exception of the two island seats, the recommendations are each seat should be no smaller than 71,031 voters and no larger than 78,507.

UK constitution minister Chris Skidmore said: "Our democracy and parliamentary system needs to represent everyone equally.

"That's why the independent Boundary Commission for Scotland is proposing measures to achieve equal-sized constituencies that will ensure an equal say for each voter.

"At the same time it's important to take this opportunity to cut the cost of politics, saving £66m over the course of a parliament by reducing the number of MPs."

He added: "The case for these reforms was agreed by the last Parliament. The initial proposals published by the Boundary Commission will be subject to consultation, with final recommendations submitted in autumn 2018.

"These will be subsequently scrutinised and debated by parliament.

"We are committed to ensuring fair and equal representation for the voting public across the UK is in place by the next general election."

Scottish Parliament constituencies will not be subject to the changes and will instead be separately reviewed by the Scotland Boundary Commission, expected to start in 2018.