Legal & General's claims to have written £8.1bn of mortgage business last year have been met with surprise from rivals.
Rival experts say L&G's results, up from £7.2bn in 1999, seem high and are questioning the way they are calculated.
Scottish Amicable national mortgage manager John Malone is surprised by the figure which gives L&G a 6.8 per cent market share.
L&G says two-thirds of the loans were arranged through its mortgage club, its lenders' panel which negotiates deals.
ScotAm and Allied Dunbar make up the other two of the top three mortgage clubs in the UK. Industry sources query the difference between the three, with ScotAm at around £6bn and Allied Dunbar between £4bn and £5bn.
Malone says lenders on ScotAm's Premier Mortgage Service say they put through more business with Premier than with any other mortgage club in 2000.
Malone says: “After reading L&G's mortgage club figures in Money Marketing last week,I was somewhat surprised to see the totals they have received.”
L&G PR manager (housing) Peter Timberlake says: “We provide our business partners with services and support systems enabling them to source and arrange mortgages with all UK lenders. L&G's figures include this business as well as that done via the club.”