Rathbones saw its assets under management increase to £47bn thanks to the acquisition of Scottish wealth management firm Speirs and Jeffrey.
In its results for the third quarter of the year Rathbones revealed its assets increased by 18.5 per cent in the three months to the end of September, from £39.9bn.
Excluding the acquisition, Rathbones said its assets grew by 1.8 per cent during the quarter.
Rathbones paid an initial £104m to buy Speirs and Jeffrey in August, which contributed £6.7bn to the asset growth.
Philip Howell, the chief executive of Rathbones, said: "This increase in scale places us in a strong position to continue to improve our service to clients and, mindful of recent volatility in investment markets, to maintain our disciplined investment in the business."
Assets under management in the unit trust business were £6bn.
Net operating income was £70.8m, an increase of 13 per cent on the same three months in 2017.