The head of Standard Life's UK operation, Trevor Matthews, has resigned.
Mr Matthews has accepted a new post at Friends Provident
He will take up a new post as chief executive of Friends Provident.
The announcement is seen as a major blow for the Edinburgh insurer, which had seen its share price affected by uncertainty over Mr Matthews' future.
He is credited with leading the company's transformation from a with-profits company to one focused on higher-margin products like Sipps.
The resulting growth in business saw Standard Life through a very strong first year as a stock market company.
The loss of Mr Matthews, who was appointed in 2004, is seen as another blow for Standard Life after it failed to do a deal with Resolution last autumn.
Speaking about his new job, Mr Matthews said: "Whilst the current environment is challenging, I plan to put past uncertainties behind and, with the team, profitably grow and develop the business.
"There are many opportunities, and Friends Provident is very well placed to capitalize on these."
It is not yet known when Mr Matthews will take up his new post.
Standard Life chief executive Sandy Crombie will lead the company's UK financial services until Matthews is replaced.
On Wednesday, Standard Life reported a 20% drop in fourth quarter UK sales as market volatility hit the group's domestic business.
The company posted £2.92bn of UK life and pensions sales in the last three months of 2007, which was below the £3.04bn expected in the market.
However, the fourth quarter performance failed to derail full-year growth in the UK, with life and pensions new business up 15% to £13.17bn.