Sales of investment funds stalled last month as investors re-evaluated their portfolios, industry figures show.
The IMA said investors were worried about stock market volatility
The total value of UK investment funds was £468bn in December, a rise of just 1% on November, said the Investment Management Association (IMA).
Gross investment sales fell to £8.4bn, but investors withdrew more than they paid in, leaving the monthly net sales total negative at minus £858m.
The IMA says the continuing credit crunch is damaging investors' trust.
December was the second consecutive month when more money was withdrawn than invested.
In contrast positive net sales of £1.7bn were recorded in December 2006.
Banks and building societies have already reported taking record cash deposits in the last quarter of 2007, largely as a result of the run on Northern Rock.
The IMA figures showed that sales of tax-free share Individual Savings Accounts (ISAs) also dropped in December. They were at £491m, 20% less than the figure for November.
When the amount of money withdrawn from ISAs in the month was taken into account, the overall increase was only £17m.
The number of share ISAs held by investors also fell to 8.12 million in December, down from 8.21 million the previous month.
"The first 10 months of 2007 saw a continuation of the strong performance of the previous year," said IMA chief executive Richard Saunders.
"In November and December however, as the impact of the credit crunch began to be felt, investors significantly re-evaluated their portfolios and the industry experienced its first overall retail outflows in 15 years.
"The year as a whole was satisfactory for the industry, but the prospect is clearly more uncertain going in to 2008," he added.
Earlier this month, the Building Societies Association (BSA) said its members took in cash deposits of more than £16bn during 2007, almost double the 2006 total of £8.3bn and the highest level to date.
BSA director general Adrian Coles described 2007 as a "bumper year".
He said this was partly a result of the problems at Northern Rock but also because, given the continuing uncertainty in the financial markets, many savers were attracted to the security offered by cash deposits.
The previous record was £13.6bn, set in 1988 when savers sought safety after the stock market crash of October 1987.