Rishi Sunak has said the minimum salary levels needed for British nationals to bring foreign relatives to the UK will rise to £38,700 in 2025, adding yet more confusion to the rapidly changing rules.

The prime minister’s comments come just a day after an initially unnoticed parliamentary answer said the much-criticised plan to more than double the threshold from £18,600 a year to £38,700 was being shelved.

Instead, the Home Office said, the minimum salary would be changed initially to £29,000 in spring 2024, with no timeline given for an increase to £38,700.

This prompted a backlash from rightwing Conservative MPs, whose anger over annual net migration figures of 745,000 prompted Sunak to toughen the rules on both work and family visas this month.

In an interview during a visit to an air ambulance headquarters in Lincoln on Friday, Sunak said the subsequent rise to £38,700, a threshold that would put being able to live together in the UK out of reach for many thousands of families, would take place in 2025.

“We are increasing the salary threshold significantly, and we are doing exactly as we said, we’re just doing it in two stages,” he said. “So it will go up in a few months’ time and then it will go up again, the full amount, in early 2025.”

Sunak’s stated timetable is different to that set out by the Home Office on Thursday evening. Even though this did not give dates beyond the rise to £29,000, it said there would be two more stages: to £34,500 and then finally to £38,700.

By Friday evening the Home Office had updated its factsheet about the policy to confirm the spring 2025 date. This said the interim stage of a £29,000 threshold would also happen, but did not say when.

The Home Office and Downing Street were contacted for clarification.

While current polling indicates Sunak and the Conservatives are likely to be out of office by spring 2025, meaning it would be a decision for another government, the seemingly accelerated timetable points to renewed worries in No 10 about anger from rightwing MPs.

In January, Sunak is hoping to avoid a rebellion from the same faction over his bill aiming to remove legal barriers to deporting asylum seekers to Rwanda.

But at the same time, moving forward rapidly on the higher income threshold will dismay campaigners and lawyers, who have warned that even the £29,000 limit will tear families apart and discriminate against those on low incomes.

The migrant-led charity Migrant Voice condemned the policy as a “cruel way of separating families”.

Its director, Nazek Ramadan, estimated that increasing the threshold to £29,000 would affect between 10,000 and 20,000 people.

She said: “Even with a partial U-turn, this festive season many of those working here will be scared that this is the last one they can stay with their families. No one should be banned from having a family based on where they were born or how much they earn.”

Ramadan added: “The existing income requirements of £18,700 are already seeing parents having to only see their children via a computer screen this winter. Increasing it, whether to £29,000 or £38,700 later, will rip more families apart.”

Colin Yeo, a barrister and writer on immigration, had said the change to an initial threshold of £29,000 amounted to a “terrible” compromise. Writing on X, he said: “Now the govt announces its ‘climbdown’: the outrageous new rule won’t apply to spouses and partners already sponsored, only those applying for the first time. AND the income requirement will initially be lower: ‘only’ £29,000.

“It still massively discriminates against northerners, Scots, the Welsh, women, carers. It’s still way higher than the minimum wage. It’s a brutal interference by the government with the private lives of its citizens.”

The campaign group Reunite Families UK agreed. In a statement it said: “£29,000 is still very high for most families – it excludes over half of the population from sponsoring a foreign spouse and is much higher than the minimum wage so those on lower salaries are still being told their family is not welcome here.

“It’s baffling why the MIR [minimum income requirement] is now going to be raised incrementally – the process is already complicated enough without this too.”

The rules on salary thresholds are part of a wider crackdown intended to reduce net migration by about 300,000. They were set out by the home secretary, James Cleverly, after fury among some Tories when data released in November showed net inward migration had been 745,000 in the year to December 2022.

The increase in the family visa salary requirement was expected to contribute only about 10,000 to the overall planned reduction.