The online mortgage company says borrowers with loans-to-value of up to 125 per cent taken out a year ago are typically on rates between 6.05 and 6.55 per cent.
But mform.co.uk is warning they may have to go on to the standard variable rate of 7.49 per cent.
mform.co.uk adds that even borrowers with loans-to-value of up to 80 per cent are likely to get a better deal by shopping around.
The website says that a two-year fixed rate remortgage from the Principality for a £150,000 mortgage will cost the customer £23,914.80 including all fees, compared to the best deal from Lloyds which costs £24,597.92.
It adds that the best three-year fixed rate by Norwich & Peterborough costs £35,510.88 over 36 months, compared to Lloyds’ cost of £36,183.92.
mform.co.uk marketing and business development director Francis Ghiloni says: “The Lloyds TSB offer is a good move and should be looked at seriously by most of Northern Rock’s 180,000 mortgage customers. However those people with loans up to 125 per cent of their house’s value are genuinely between a rock and a hard place. The price of their house may have fallen and they won’t have built up enough equity to secure a better deal.
“Unsurprisingly Lloyds TSB is not keen on taking on people with high loans-to-value and is focusing on the most creditworthy. Borrowers should take a similarly hard-nosed attitude. What is best for them is usually to shop around.”