Experts pointed out that the average lump sum is around £6000, and likely to be needed for retirement, while those with big pensions can probably afford to help fund a deposit anyway. Mr Clegg himself admitted the maths probably only worked for 12,000 people.
It coincided with research from Saga showing one in eight over-50s already give their children or grandchildren money for a deposit to buy their first home, with 27% saying they have given them a large sum of money for a once-in-a-lifetime purchase, such as a deposit.
A report published today by HSBC, researched by the Centre for Economics and Business Research (Cebr), reveals that the "bank of mum and dad" has helped to finance more than 100,000 first-time borrowers between 2008 and 2011. "This 'family financing' has also made a significant contribution to the FTB market during this period, enabling approximately £23 billion worth of FTB purchases, or £5.6bn a year," says the report.
In the last year alone, £5.3bn or 18.7% of all FTB transactions would never have taken place without family financing, according to the report's estimates. It predicts that by 2017 that figure will still be over £5bn, but claims that by then 89% of FTB loans will again be bank funded.
Daniel Solomon, Cebr economist, says: "Mortgage lending to British FTBs fell off a cliff during the financial crisis. To some extent, families have moved in to fill the gap, providing gifts and loans to their first-time buyer relatives."
Peter Dockar, head of mortgages at HSBC, said: "We have remained open for business and will continue to support first-time buyers so they have the opportunity to become home-owners in their own right." He said the bank had committed £4bn to the FTB market this year.
HSBC's 90% mortgages, which attract a "best buy" tag from moneysupermarket.com, come in at 4.89% for a five-year fixed rate, or 4.49% for a tracker set 3.99% above base rate but with no early repayment charge. Both have arrangement fees of 4.49%. From the same banking stable, the website also highlights First Direct's 4.29% for two years with a £900 fee, or a tracker set 4.09% above base rate (no fee, no exit charge).
Other competitive fixed rates come from mutuals Chelsea (part of Yorkshire building society), the Hanley building society and Britannia (part of Co-operative Bank).
For joint applications by graduates, there is a "share to buy" 90% mortgage priced at 3.79% with no fees and no strings, and a minimum purchase price of £75,000.
Clydesdale Bank has a pricier rate of 5.89% fixed for five years with a £999 fee. RBS lists a similar product at an even higher 6.19%, according to Moneyfacts, while at Lloyds TSB Scotland the 90% loan to value rate is shown as 6.89%.
Last month, Leeds building society launched a new shared ownership mortgage on a three-year fixed rate of 5.99% for those unable to raise the full deposit needed on a property. Sharron Fairley at the Leeds office in Glasgow said: "We are all well aware of the difficulties facing first-time buyers in Glasgow buying a home.
"They can often struggle to meet the full asking price or their current income is insufficient to support a full mortgage. This shared ownership product facilitates that first step, and provides a starting point to staircase up to full home ownership."
Next week sees the roll-out of the scheme which the Scottish Government hopes will go some way to filling the FTB funding gap.
The MI New Home scheme provides a Scottish Government guarantee to lenders and house builders, to encourage them to lend to new buyers on new property, and it could help 6000 borrowers.
Nationwide and RBS have already signed up to the scheme, to be followed by Lloyds Banking Group, along with 12 builders: Bancon, Barratt, Chap, Charles Church, David Wilson, Lovell, Merchant, Miller, Persimmon, Springfield, Stewart Milne and Taylor Wimpey.
According to the Council of Mortgage Lenders, there were 44,000 loans advanced for all home purchases in Scotland in 2011 compared to 105,000 in 2006 – a fall of 60%.
Philip Hogg, chief executive of Homes for Scotland which runs the scheme, said: "The scale of the problem is highlighted by the fact Scottish home buyers are having to find an average 25%. This equates to nearly £40,000 based on an average [Scottish] home price of £156,410."
Meanwhile, Mr Clegg's proposals are unlikely to see life beyond the LibDem party conference.
Joanne Segars, chief executive of the National Association of Pension Funds, said the idea made her feel uneasy. "A pension can only be spent once and this policy could end up leaving retirees out of pocket."
Dr Ros Altman, director-general of Saga, said the plan was "a very strange idea". Terry Smith, founder of the Fundsmith investment group, was more forthright, describing Mr Clegg as "brain dead". He added: "The 'idea' of people who mostly already have inadequate pension provision using part of it to give their children a stake in what are almost certainly still over-priced houses beggars belief."
One of the first house builders to sign up to the MI New Home initiative, Stewart Milne Homes, is now offering 95% mortgages on all properties across Scotland, up to a value of £250,000.
Its existing deferred payment plan for new borrowers helped Michael MacLugash, 24, an accountant with an oil services firm in Aberdeen, and Emma Simpson, 25, move into their first home this year. They were both living with parents and needed to move closer to work, and were keen to invest in a property rather than just renting.
The couple decided to look at new-build properties due to the financial support available, describing the need for an average 20% deposit as "the main blocker" to securing a new home.
They chose Stewart Milne's Vision development in Aberdeen, and opted for deferred payment.
Mr MacLugash says: "As first-time buyers, we were dubious about the ensuing process and didn't really know where to start, so we were pleased to find the house builder offering a full support service throughout."