Middle aged children paying off their elderly parents' mortgage might seem like a completely ludicrous idea when we're used to older generations assisting struggling youngsters, but a new trend is brewing in property finance.

The complete reversal of the 'Bank of Mum & Dad', however, is not all it seems.

Rather than cash-strapped mature parents turning to their offspring for financial assistance, the 'Bank of Son & Daughter' is more about passing down wealth, freeing lump sums of cash and reducing inheritance tax.

The basis of the deal revolves around parents releasing equity in their property to hand down to children without facing tax penalties. This requires older people taking out new-style mortgages aimed at those over the age of 65 and the children chipping in to help pay off the monthly repayments.

The matter isn't as straightforward as taking out a normal mortgage though. Specialist wealth planning and financial advice would be required, but the foundations are being laid by lenders to offer more mortgages to those past retirement age.

There are lingering questions, however. If you were in your 40s or 50s and needed a big injection of cash as a lump sum, would you feel comfortable about asking your parents to remortgage to free equity? And would you be happy to help with the subsequent mortgage repayments?