LONDON (Reuters) - Fund manager F&C Asset Management (>> F&C Asset Management plc) said it continues to face "significant headwinds" after a net outflow of 19 billion pounds in 2013.

The outflow was attributable to the withdrawal of 20.3 billion pounds of money managed for strategic partners, which was partly offset by an inflow of 1.3 billion pounds from consumer and institutional clients, the company said.

"While 2013 has been a year of progress, we also acknowledge the financial headwinds that still face our business," Chief Executive Richard Wilson said.

"The withdrawal of assets from strategic partners will continue to impact upon revenues, while the development of our consumer and institutional business will take time and investment."

The outflows amount to an annualised loss in revenue of 35.5 million pounds, of which 11.3 million pounds is reflected in 2013 earnings, the company said.

Net revenue for the group was 241.2 million pounds, down from 243.5 million pounds in 2012.

However, the group noted that cost-cutting targets have now been achieved, helping to strengthen the operating margin to 36.9 percent from 29.2 percent a year earlier.

F&C shareholders are due to vote on a takeover offer from Bank of Montreal (>> Bank of Montreal), which offered 708 million pounds for the company in January.

The deal has the blessing of F&C's largest shareholder, British insurer Aviva (>> Aviva plc), though the company's second-biggest investor, Standard Life (>> Standard Life Plc), has said it may support a rival bid if one emerges.

Meanwhile, activist U.S. investor Elliott Management Corp has acquired derivatives equivalent to a stake of almost 11 percent in F&C, adding to expectations that shareholders may seek a higher bid from Bank of Montreal or a rival.

F&C management reiterated its support for the Bank of Montreal offer on Thursday, arguing that the deal would pay shareholders "an attractive premium against the potential medium-term standalone prospects and valuation" of the company.

(Reporting by Chris Vellacott; Editing by David Goodman)