Northern Ireland is the most affected region, where repossessed properties sold for 42% of their value between 2008 and 2013.
Scotland, the North West and the North are in joint second place, where properties sold for 63% of their true cost.
Damian Riley, director of business intelligence at HML, said: “Many repossessed Britons do not realise that they may still owe their former mortgage lender money if the property sold for less than the value of their mortgage.
“As our recent shortfall debt regional figures noted, over 188,000 former UK mortgage holders still owe their former mortgage lender money, with an estimated 83% of repossessions in shortfall, with the average shortfall £43,000.
“One reason for the differences in shortfall positions across the UK is the ‘forced sales discount’ i.e. the reduction in sale prices of homes that have been repossessed, compared to the wider market.
“This observed drop in price is as a result of the deteriorating condition of empty repossessed properties once utilities are disconnected and general maintenance reduced or stopped.”
The least affected region is Greater London, where repossessed properties sold for an estimated 78% of their true market value.
Riley added: “The regional figures show there is a North/South divide, with repossessed properties typically selling for well below market value more in the North than in the South.
“At HML, we believe that assisted voluntary sales are one way to help reduce the shortfall on a sale price.
“This is where we help our clients’ struggling mortgage borrowers remain in their homes while a sale completes - rather than face repossession and potential eviction - by finding the best price, arranging for their lender to cover the costs of conveyancing and solicitors and helping the borrower find affordable living arrangements.”