The Conservatives may have been able to avoid entering a coalition with the Liberal Democrats had the 2010 election been carried out using the new proposed boundaries for the United Kingdom, analysis by the Guardian suggests.

Publication of new electoral boundaries for Wales comes in the wake of similar proposals for the other parts of the union and allows, for the first time, modelling of the effects of the proposed changes across the country.

The proposals are aimed at equalising the size of different constituencies across the country, because the current uneven constituencies are seen by many Conservatives as favouring their Labour rivals.

The plans also reduce the total number of seats in the House of Commons from 650 to 600.

Boundary changes UK: click image for interactive map

Using the voting results of the 2010 general election with the proposed boundaries, the model predicts the Conservatives would have won 296 seats – five short of a majority in the smaller House of Commons that the new rules would create.

With the Conservatives' longstanding allies in Northern Ireland, the DUP, projected to have won seven seats, the Conservatives could have commanded a slim majority without having to enter into coalition with the Liberal Democrats.

Labour would have lost twice as many seats as the Conservatives. They would have been left with 237, while the Liberal Democrats would have lost the most relative to their size as a party with 43 MPs, rather than 57 under the current system.

The model projects the total votes from old constituency boundaries on to the newly proposed constituencies, and uses the assumption that voters for each party are spread evenly within each constituency. That is a relatively crude simplification but one which has generated results consistent with those of professional psephologists when tested against the new English boundaries.

Lewis Baston, senior research fellow at Democratic Audit, said the Guardian's projections showed the size of the challenge faced by the Liberal Democrats because of the reforms.

"Most sensible estimates show these effects, and as ballpark figures these are pretty good – though these boundaries are not the final word as we don't yet know how the boundary commissions will respond to consultation," he said.

"There are two reasons the Liberal Democrats are particularly at risk. The first is that Liberal Democrats have an average majority that is smaller than the other parties, so less able to cope with adverse voters coming in.

"The second is Liberal Democrat seats tend to be yellow islands in seas of red or blue, meaning changes to the boundaries tend to bring in opposition voters."

Baston added that the slump in Liberal Democrat support since the 2010 election could make the situation substantially worse.

"If Liberal Democrat support is 10% to 12%, that's catastrophic. At 18%, they could expect to hold on to half or more of their current seats."

The primary consultations on new boundaries for England, Scotland and Northern Ireland have now closed. Results will be published in spring this year, while Wales will consult on its new proposed boundaries for the next 12 weeks.