That compares to 18 per cent in February and 16 per cent in the same month last year, leading analysts to suggest a direct link with the recent Bank of England rate rise to 5.25 per cent.
According to CML, the number of first-time buyers is dropping as interest rates increase, with eight per cent fewer (33,100) getting on the property ladder in March than did 12 months earlier.
But the latest data does suggest that many new homeowners are seeking to reduce the impact of future rate rises by opting for fixed-rate loans when buying their property.
"With a rise in interest rates widely expected later this week it is encouraging that those first-time buyers who are getting a foot on the property ladder are opting for fixed-rate products," CML director general Michael Coogan said.
"Affordability constraints continue to be a barrier to home-ownership for many first-time buyers. Mortgage lenders are trying to help by offering innovative products where appropriate but will want to ensure lending remains prudent."
Responding to the survey, senior economist David Stubbs of the Royal Institute of Chartered Surveryors (Rics) said it highlighted the "huge barriers to home ownership" which first-time buyers face.
"They have to save large amounts for deposits, stamp duty and fees and then must spend an ever increasing share of their income of servicing the massive mortgage needed to buy a home," he said.
"With higher interest rates on the way, the situation looks certain to deteriorate further in coming months."
The Bank of England is widely anticipated to lift base rates to at least 5.5 per cent when it announces its decision for May later this week.
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