M&G Prudential has lost a £6.1 billion institutional mandate.
The news was revealed in a trading update from its parent, Prudential, covering the first nine months of the year.
The mandate was described as 'low margin' by the firm.
The loss contributed to external net outflows of £5.6 billion for the first nine months, versus inflows of £9.9 billion for the corresponding period of 2017.
External funds under management were £157.4 billion at 30 September, a fall from the £163.9 billion they stood on at the end of December.
Earlier this year, the recently formed UK and European M&G Prudential announced it would be splitting off from parent company Prudential into a separately London-listed FTSE 100 business. The parent company would focus on the rising Asian market, as well as the US.
Prudential said it is ‘making good progress’ on the demerger, which is ‘on track’.
Overall, M&G Prudential's total funds under management fell from £350.7 billion to £334.5 billion.
There was more positive news for M&G Prudential’s PruFunds range, which saw net inflows of £6.6 billion in the first nine months of 2018, taking the funds’ assets to £42.9 billion.
The PruFund, which acts like a with-profits fund, has grown by 19% since the start of the year. This helped increase M&G Prudential’s new business profit to £277 million.