Its figures show just six of the top 50 two-year fixed rate 85% LTV deals are offered by the largest lenders, equating to 12%.
For its research Moneyfacts.co.uk looked at deals from lenders such as Halifax, Cheltenham & Gloucester, Lloyds TSB Scotland, Santander, Alliance & Leicester, Abbey for Intermediaries, Nationwide Building Society, Woolwich, Royal Bank of Scotland, NatWest, Northern Rock, HSBC and First Direct.
It says the largest lenders are most competitive in the two-year tracker market, but this still only equates to less than half of the top 50 deals.
Michelle Slade, spokesperson for Moneyfacts.co.uk, says the figures show that biggest isn’t always best and in many cases the most competitive mortgage deals are not being offered by the largest mortgage lenders.
She says: “Larger lenders appear to be concentrating on offering more competitive deals to borrowers with at least a 25% deposit.
“When selecting a new deal, borrowers should ensure they look at the true cost of the mortgage, including the fee.
“A deal with a low rate, but a high fee could work out more expensive than a slightly higher rate with a much lower fee.
“Some of the lowest rates on the market charge a percentage fee, which can work out very expensive if you have a sizeable mortgage.
“In a time when the cost of mortgages continues to rise, these results show that it is even more important for borrowers to shop around to get the best deal.”