Two hundred Labour seats – more than 85% of the party’s total – could be affected by the review of parliamentary boundaries due next month, according to a detailed analysis of the review’s likely impact.

Up to 30 Labour seats could disappear altogether, says Lord Hayward, an analyst widely regarded as an expert on the boundary review, while the rest will see their composition altered in some form.

Although the changes will also affect the Conservatives, Hayward, a Tory peer, said his analysis of demographics in the UK concluded that Labour is over-represented.

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“The party that will suffer most is the Labour party because such a high proportion of their current seats are well below the required quota, particularly in Wales, the north-east and parts of the M62 corridor,” he said.

The changes, initiated by David Cameron, which will cut the number of MPs by 50 to 600, aims to ensure that each person’s vote is of similar value by equalising the number of registered voters in each constituency to within 5% of 74,769. A higher proportion of Tory seats are currently within the range, so only between 10 and 15 of the party’s seats are expected to disappear.

MPs of all parties face the prospect of battling it out with colleagues to retain a seat, but anxieties will be particularly acute within Labour, where anti-Corbyn MPs fear that the necessary reselection contests could be an opportunity to reshape the parliamentary party in Corbyn’s favour, if he retains the leadership. “This will have implications for large numbers of Labour MPs who may well have to compete against each other for reselection,” Hayward added.

Hayward’s estimates have already resulted in a backlash from Labour, who have accused the government of “gerrymandering”. A spokesperson for Rosie Winterton, Labour chief whip, reacted angrily.

“Lord Hayward’s comments – a key architect of the Conservative’s boundary changes – that reducing the number of elected members of parliament by 50 will benefit the Tories’ electorally, is further evidence that the sole motivation for these changes is a partisan plan to give the Tories’ an unfair advantage at the expense of democracy. Simply put, this is gerrymandering,” he said, urging Theresa May to think again about the policy, which he called “a major constitutional change”.

Proposals will be released by the Boundary Commissions for England, Wales, Scotland and Northern Ireland during September, but Hayward has looked at the possible implications ahead of the actual data. Maps published on Sunday show that the vast majority of seats that fall within the new range are held by the Conservatives, while three in four Labour seats are below the required size, many in urban areas. Hayward analysed the impact on each region to come up with an estimation.

His figures suggest that of the 50 seats that disappear, the Conservatives will lose between 10 to 15, which is 4.5% of their total. That could still prove to be a headache for May given that it is more MPs than the party’s majority.

However, Labour is on track to lose between 25 and 30, which is 13% of their total. Other constituencies will be significantly changed with some turning from safe Labour seats to marginal ones, harder for Labour politicians to hold on to.

Other parties, including the SNP, will also be hit.

Hayward argued that there had been an unfair advantage for Labour previously and that it was right to redress the balance.

“The intention is to produce equally sized constituencies and then each vote would be fairly represented as against the unbalance that exists at the moment,” he said.

Labour, however, also believes that Brexit provides further justification to row back on the policy given that all 73 of the UK’s MEPs are expected to go by the end of this parliament. “In light of this, a reduction in the number of elected members of parliament is simply wrong,” Winterton’s spokesman said.

The opposition party is also angry that the boundary changes are based on the number of people on the electoral register at the end of 2015, arguing that 2m extra people signed up in the run-up to the EU referendum this year. “Worryingly, under the Tories’ plan, not a single one of those 2 million extra people will be taken into account in the drawing up of the new constituency boundaries. This is simply wrong and runs the risk of further distorting the Boundary Review Process,” he added.

Some MPs argue it is unfair not to take into account people who live in constituencies but are not signed up to the electoral register.

The SNP have also raised concerns. “In the run up to the Scottish independence referendum, the UK government said that if Scotland rejected independence we would be treated as an equal partner in a family of nations, with our views valued and respected.

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“Since then we’ve had English votes for English laws, then the Tories tried to cut £7bn from Scotland’s budget, now they want to drag Scotland out of the EU against our will, and then slash the number of Scottish MPs at Westminster by 10%,” a party spokesman said.

A similar exercise was begun in 2013 but abandoned by Cameron in the face of pressure from his Lib Dem coalition partners, and anger from his own backbenches. The Tories are hoping to avoid a repeat of the anger by offering affected MPs the chance to move into seats vacated by colleagues retiring.

Prof Ron Johnston of Bristol University, who has advised the government about boundary changes, said the existing structure of constituencies had disadvantaged the Tories. His team calculated that the 2001 election was “probably the most biased in its outcome”. If Labour and Conservatives had scored the same share of vote in that contest, Labour would still have won 142 more seats, of which 50-60 would be due to size variations. “So yes, the system was stacked against the Tories.”

A spokesperson for the Boundary Commission for England, which will publish its maps on 13 September, said a parliamentary act dictated that the 2015 data was used. “Many current constituencies are not within the permitted electorate range, and some that are may still need to change, to enable neighbouring constituencies to be suitably adjusted,” they added.