Buy-to-let investors with mortgages from now-defunct lenders risk being trapped on uncompetitive rates for life, thanks to draconian new rules imposed by the Bank of England.
Brokers and landlords are calling on lenders to be "flexible" when interpreting the Bank's recommendations about buy-to-let borrowing, which came out last month.
When laying down strict new criteria for lending, the Bank clearly said that the new regime should not be applied to existing borrowers who wish simply to switch to a better deal, rather than borrow more.
But lenders are already indicating that they are unlikely to take on borrowers who do not meet the new criteria.
This could leave thousands stranded on high rates - just at a time when higher taxes pose an additional threat to the viability of their businesses.
Britain's second-largest buy-to-let lender, Nationwide, confirmed to Telegraph Money that it will not accept remortgagers from other lenders, unless they meet the new, tighter conditions.
The mutual lender increased its income requirements for landlord borrowers earlier this year, and now requires borrowers to receive 145pc of their mortgage costs in rental income, up from 125pc.
Lloyds, the largest buy-to-let lender, refused to say whether borrowers remortgaging from other lenders would be allowed to apply under the old criteria.
In a statement rival lender Lloyds said: "We will continue to monitor the market and regularly review our policy to ensure borrowers have the right level of protection to meet their needs."
However other, smaller, lenders appear to be considering relaxing their policy.
Barclays said that before the publication of the report it would always have put remortgagers through its affordability process under its current terms, but is now reviewing this.
Yorkshire Building Society also said that it was "currently reviewing" its stance.
The FSA, now the FCA, made similar restrictions to homeowner mortgages in 2014, also allowing lenders to accept business from other lenders under old, less restrictive conditions.
Few banks did this immediately, though some loosened their stance later on.
Simon Checkley, of mortgage brokers Private Finance, said that the Bank of England had given lenders the opportunity to accept customers from other firms - and he was hopeful that they take it up.
He said: "For pound-for-pound remortgages, banks do have the scope to be flexible.
"I hope with this that lenders might be a bit more flexible - it could be a way out for those borrowers who have been stuck and unable to remortgage."
Potentially worst off are those tens of thousands of borrowers who have mortgages with lenders including Mortgage Express and Cheltenham and Gloucester, which are no longer advancing new loans to anyone.
Existing customers who cannot move to another lender will not be able to find a new deal with their existing provider, either.
Others are able to remortgage, but have a very limited choice of higher than average rates.
Borrowers who reach the end of a fixed-rate deal, for example, and then roll over on to a standard variable rate, could find they are paying well over 5pc. This is considerably higher than many of the deals available to those meeting the new criteria.
Lenders have been increasing the amount of rent landlords need to receive in relation to their mortgage liabilities since earlier this year, in line with the Bank's consultation paper announcing that it would be tightening regulation on buy-to-let lending.
The tax double-whammy
From next year a new tax regime for landlords will also limit the amount of mortgage interest relief higher and additional-rate taxpayers can claim.
By 2020 the ability to deduct mortgage interest from rental income when calculating a tax bill will be removed completely, and replaced with a 20pc tax credit.
The new tax regime will send many landlords with large mortgages and low yields into a loss-making position.
- Are you a mortgage prisoner? Get in touch: olivia.rudgard@telegraph.co.uk