Lenders stand accused of launching mediocre products to avoid being swamped by business in case the millennium bug causes chaos.
Mortgage brokers believe some lenders have deliberately stacked their mortgage ranges with moderately priced, unattractive deals.
They are aiming to keep sales low, avoiding having to process high volumes of business at the end of the year amid fears they may not be Millennium bug compliant.
It is understood most lenders have placed specialist "clean-up" squads on red alert, and banned them from leaving the country between Christmas and New Year in case processing problems arise.
Portman Building Society has banned its the staff of its Bournemouth headquarters from leaving the country over the holiday period.
IFAs say lenders that have taken their foot off the pedal will lose large volumes of business to Halifax and Abbey National, as both have launched a range of competitive fixed and capped rate deals in a bid to boost their market share before the year ends.
Chase de Vere Mortgages managing director Simon Tyler says: "Some lenders have suggested they don't want to be working at peak levels towards the end of the year due to holidays and the fear of the millennium bug."
John Charcol technical manager Ray Boulger says: "There is an even wider margin between the best deals and worst deals making it even more important for people to shop around.
"Some of the larger lenders such as Halifax and Abbey are clearly trying to boost their market share before the end of the year by launching loss leading fixed rate mortgages, while others are looking to tail-off their business to reduce the strain on their processing systems."