The end of the stamp duty holiday will leave hundreds of thousands of buyers poorer and bring the housing market boom to a crashing halt, experts have warned.

Campaigners are calling on Chancellor Rishi Sunak to extend the tax break from its current end date of March 31 to prevent chaos from engulfing the market and derailing Britain's post-Covid recovery.

Around 325,000 buyers mired in coronavirus-related sales delays will miss out on savings of up to £15,000 if the tax break is scrapped, according to data company TwentyCi.

It is feared that more than 100,000 of them could then pull out of deals as a result – potentially hammering sales volumes, harming the economy and hitting prices.

The Telegraph is today launching a Stamp out the Duty campaign to support the homeowners set to be caught out by the rise, calling on the Treasury to avoid penalising thousands of homebuyers at a time when mortgage lenders are already demanding vast deposits and household finances have been battered by the pandemic.

Chris Etherington, a partner at tax service provider RSM, said: “There is little logic in doing these measures and then pulling the rug out from under the feet of estate agents by having the cliff edge of the stamp duty holiday.”

Phil Spencer, the TV property expert, said: “There is a big tsunami of deals building up. If the Chancellor really does stop the stamp duty holiday I just think chaos will ensue.

“People will try and renegotiate up and down chains, and it only takes one person in the chain for four or five sales to fall through. The whole thing will come to a crashing halt and deals will fall off the shelf left, right, and centre."

The cliff edge created by the end of the holiday could lead to a crash in transactions. Property website Zoopla has forecast a 20pc to 30pc drop in sales between April and June this year, and a 10pc hit for the last six months of 2021. House sales stimulate the economy , so any drop on this scale would likely show up in GDP.

In July, Mr Sunak raised the nil-rate stamp duty band in England and Northern Ireland from £125,000 to £500,000, meaning nearly 90pc of transactions became tax free. Demand boomed despite chaos in the wider economy.

TwentyCi data shows there are now more than 536,000 agreed sales progressing to completion. This number is nearly double the volume of sales that completed in the same three-month period in 2019, and it is increasing. In the first week of this year, agreed sales were up 16pc compared to the same period last year.

Glynis Frew, chief executive of Hunters estate agents, said: “The current lockdown has only added to this bottleneck. I would implore the Treasury to consider an extension.”

Beth Rudolf, of the Conveyancing Association trade body, said: “If they don’t extend the deadline, hundreds of thousands of sales will fail to complete. The property market will literally drop off.”

Massive demand and the pressures of lockdown mean logistical delays are escalating. Leasehold and cladding complications have also sparked a wave of post-valuation queries, Ms Rudolf said. The average transaction now takes 20 weeks to complete, up from 12 weeks before the pandemic started.

This means a buyer who agreed a sale after October has little hope of making the tax deadline.

Iain McKenzie, of the Guild of Property Professionals, which represents estate agents, suggested that up to a third of buyers who miss the deadline will pull out of their deal altogether. This would be equal to more than 100,000 people.

Tom Bill, of Knight Frank estate agents, added: “Buyers and sellers will renegotiate on pricing up to the £15,000 saving.”

The ensuing chaos will cause businesses to collapse, added Ms Rudolf. Conveyancers typically work on a “no sell no fee” basis.

She said: “They won’t get paid for work they have done. Of course [companies] will go under, and it will be the same for estate agents.”

Rob Houghton, chief executive of Reallymoving, a home-moving services website, said many conveyancing firms have recently expanded to handle demand and hired new staff. “Their costs are up and if their revenues are not up pro rata it will be painful,” he said.

Many in the property sector have called for the Treasury to extend and taper the tax break, allowing buyers who have agreed sales before March 31 to benefit to a reducing degree depending on how long it takes them to complete.

A Treasury spokesman said: “The temporary stamp duty cut is helping to protect hundreds of thousands of jobs which rely on the property market by stimulating economic activity. Its time limited nature is what has encouraged people to take advantage of the scheme.”