“We just don’t have the money,” says Ben of the extra £6,000 to be found if the newlyweds don’t get the keys to their two-bed terrace before the stamp duty cliff-edge at the end of this month.

The special needs teacher and his partner Claire, a human rights solicitor, are among the more than 75,000 buyers in England and Northern Ireland who will have to pay more stamp duty if their purchase is delayed until April.

“Fortunately, the property we are buying is chain-free with the sellers keen to move,” says Ben of the £488,500 house they are buying in St Albans. Until 31 March their stamp duty bill is £3,175 but come 1 April it shoots up to £9,425. “We have bought a property without flooring which is already going to be a stretch to pay for.”

In England, nearly 74,000 people are likely to miss the deadline and complete in April, according to the property website Rightmove. About a quarter of them are first-time buyers. In all, this group faces paying £142m in additional stamp duty tax, and £34m of that bill will be shouldered by first-timers. The changes do not affect Scotland and Wales, which have different property taxes.

Lee, who is buying a three-bedroom house in Coventry with his partner, is “desperately hoping” to complete before the deadline. He was among the more than 80 people who responded after the Guardian asked how the end of the stamp duty break would affect them.

“Otherwise we will lose £2,500,” says the 45-year-old psychotherapist of their £300,000 purchase. “That money is really needed to decorate the property. I’m a first-time buyer but my partner isn’t, so I’ve also lost out on any of the benefits. This feels really unfair as it has been a real struggle to afford a home.”

It is now looking “highly unlikely” that the paperwork will get done in time due to delays on the seller’s end. “This may mean we need to renegotiate the price,” says Lee. “Obviously this may jeopardise the sale. We heard rumours of a possible delay being announced in the spring statement, so are holding out hope for that.”

At present, buyers of homes costing less than £250,000 do not pay any stamp duty because Kwasi Kwarteng temporarily doubled the starting threshold in his infamous 2022 mini-Budget.

Kwarteng also raised the exemption level for first-time buyers to £425,000 on properties costing up to £625,000. It had previously been set at £300,000 on homes costing less than £500,000. On 1 April, the thresholds revert back.

The reset means that from the start of next month – unless the chancellor, Rachel Reeves, grants a reprieve in her spring statement on Wednesday next week – the average home-mover in England and Northern Ireland faces an extra £2,500 in stamp duty costs.

The hardest hit will be first-time buyers of homes priced between £500,001 and £625,000. They are mainly in London and the south-east where property values are highest. Overnight, up to £11,250 will be added to this group’s costs.

At 161 days, or just over five months, it now takes about a month longer to buy a house than it did before the pandemic. With his £400,000 offer on a maisonette in south-east London accepted back in November, David “wasn’t expecting the deadline to be an issue”. But now he is worried.

“My solicitor is telling me that the mortgage lender is saying their cut-off is a week before the date [31 March] which I do not understand at all,” David says.

If his deal slips into April as a first-time buyer he will go from paying no tax to footing a £5,000 bill. “Given how hard it is to get on the property ladder, especially in London, that’s stretching an already stretched budget,” he says, describing it as the difference between “having some emergency savings … or pretty much wiping out everything”.

With the march of property prices putting home ownership out of reach for many, the average first-time buyer is now 33 years old. They must put down an average deposit of £61,000 and typically pay £311,000 for their first home, according to the mortgage lender Halifax.

At 44, Patrick, who works in the medical technology industry in Cambridge, describes himself as a “geriatric” first-time buyer. “Every estate agent we spoke to winced when we mentioned wanting to beat the deadline, even in December,” he says. “New-builds were the only real option to guarantee beating the deadline but we didn’t find one that fit the bill in time.”

He adds: “We were warned that surveyors and conveyancers and the whole pipeline is backed up and moving slowly … We will be paying the full rate and on a property costing £510,000, the difference is just shy of £11,000.”

What “really bites”, says Patrick, isn’t the increase of stamp duty rates, or even the massive drop in first-time buyer relief from £425,000 to £300,000, “it’s the fact that at £500,000 you lose all stamp duty relief”.

While £500,000 is a lot to spend on a property, in the south-east and around Cambridge it is not a big budget it you want “any space at all”, says Patrick. “A two-bed flat in Trumpington, where we rent, costs £460,000-ish. So, we have had to bite the bullet and ask for yet more help from parents – not at all humiliating at 44!”

Meanwhile, in east London, father of two and first-time buyer Sultan is waiting nervously to see if his purchase of a fixer-upper bungalow will get under the wire. If it doesn’t, the family who are living with parents will have to pull out. “The motivating factor was to take advantage of the first-time buyer discount.”

“Before the deadline our stamp duty liability is £1,750, after it’s £8,000,” says the 42-year-old charity consultant whose £460,000 offer was accepted in October. “We never expected for completion to take this long, therefore, we didn’t budget in the extra stamp duty.”

However, the mortgage application dragged on and after a building survey highlighted serious problems Sultan sought a price reduction. “We aren’t close to an agreement yet and I’m worried that we might not make the deadline.”

Dan, a Tate archivist, is also facing an agonising wait. He is buying a one-bedroom flat in south London with his girlfriend and the £370,000 purchase had been going to plan. But “over the past few weeks we’ve started to sweat”, says the 33-year-old.

The couple are waiting on one document (a communal area fire risk assessment) but the management company cannot find it. “It will be sickening to have to pay £3,500 to the Treasury because of one document. That’s a bed and a sofa for us,” says Dan. “We’ve saved for years for this flat. It feels arbitrary and punishing from a Labour government. All properties in London are going to come in over £250,000.”

As the cliff-edge approaches conveyancers, and property lawyers and working late nights and weekends to get deals done but are dealing with pressure cooker conditions.

One first-time buyer told us she was worried her solicitor’s heavy workload could derail the purchase of a £460,000 maisonette in south London. “They are inundated with calls and emails from others who also want to meet the deadline.”

Missing the deadline would mean a “massive hit” of £6,250, she says. “The price limit for tax relief for first-time buyers in London is totally unrealistic. We’re buying a two-bedroom flat in Tooting and there was nothing on the market for less than £450,000.”

The pain is perhaps keenest for buyers in long chains where progress rivals Charles Dickens’s Jarndyce v Jarndyce. “I’m not just concerned about the financial impact of this delay on me,” says Sue, who runs a sustainability charity. She is selling up in south London and downsizing to a “little two-bedroom house” in Buckinghamshire three minutes from her daughter.

“It’s an impact on everyone in the chain,” she says. “For me it’s £2,500. This would pay for our family holiday with the grandchildren this year. For my purchaser it’s £2,500: a young couple with a baby. For their first-time buyers it’s over £5,000. For the person I am buying from its £2,500. And so on.”

Some of the readers’ stories have had happy endings, though. The stars aligned for Ben and Claire, who celebrated an 11th-hour exchange on Tuesday and move on 24 March. “Just in time,” says a relieved Ben.