The five-year fixed rate is now averaging 6.47 per cent, down from 6.72 per cent at the start of August.
Similarly, 2-year fixed rates are now averaging 6.66 per cent, compared to 6.88 per cent at the start of the month.
This reverses the summer trend of increasingly higher rates, fuelled by a number of Bank of England rate rises.
Indeed, five-year fixed rate buy-to-let rates surged from 5.52 per cent in May to 5.76 per cent on 1 June, before reaching 6.43 per cent in July.
A similar trend has been observed in the residential sector, with 2-year and 5-year fixed rates falling by 0.11 per cent and 0.10 per cent respectively since this month.