Voluntary payments into mortgages more than doubled in July, August and September from the previous 12 months, data from non-bank lender Firstmac shows, raising the question whether consumers will save, rather than spend, extra cash handed to them in last week's budget.

Firstmac's analysis of its direct retail mortgage book shows the level of additional payments made by borrowers jumped to an average 10.2 per cent of the portfolio in the past three months, compared with the monthly average payment of 4.8 per cent last year.

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