The gap between mortgage rates offered by the big banks and the lowest rates in the market has widened over the past year, according to comparison site Mozo.The average variable rate for the big banks is currently 4.86 per cent (NAB's 4.15 per cent rate is the lowest of the four), compared with 3.84 per cent from iMortgage Fusion 80.The gap between the average rate of the big banks and the lowest rate in the market is 102 basis points. Mozo said that this time last year the gap was 84 bps.Mortgage Choice chief executive John Flavell said lenders were offering owner-occupier borrowers a range of incentives, including rate discounts, cashback offers and fee waivers. "In the 20 years I have worked in financial services I have never seen the level of lender competition we are witnessing now," Flavell said.