Excluding the deal to buy its biggest independent rival north of the border, Rathbone's net inflows rose 2.8 percent in annualised terms in the three months to Sept. 30, down from 3.5 percent a year earlier.

Total funds under management rose 18.5 percent to 47.3 billion pounds at Sept. 30, again almost entirely due to the addition of 6.7 billion pounds in funds from Speirs & Jeffrey.

The underlying annualised rate of net organic growth was stagnant at 2.6 percent at Sept. 30.

RBC analyst Gordon Aitken said he expected headwinds to continue into the first half of 2019 after the departure of a number of its investment managers drove outflows of client money.

Rathbone Brothers bought Speirs & Jeffrey in August for 104 million pounds, the latest move in a round of industry consolidation which has seen regulatory and other costs push smaller fund managers to join forces.

The weak organic growth and inflow numbers took the shine of 7 percent rise in underlying net operating income, which was again boosted by acquisition.

Underlying net operating income rose to 80.3 million pounds for the three months from 70.5 million pounds, a year earlier, with investment management fees rising 8.8 percent. The number topped RBC Capital Markets' estimate of 79.5 million pounds.

(Reporting by Arathy S Nair in Bengaluru; editing by Patrick Graham)