The combined group would hold close to £18bn in assets under management.

Premier Miton confirmed that it has made the bid following recent media speculation.

The asset manager said it believes the scale and cultural alignment between the respective businesses would deliver a balanced and resilient business across a diversified product offering, enabling employees of the combined businesses to maximise their potential.

Premier Miton added it is currently in “positive” negotiations with the Board of River & Mercantile.

The deal would be subject to the completion of River & Mercantile’s solutions business to Schroders.

River & Mercantile recently announced it was selling one of its solutions business division to Schroders for £230m. The division is made up of the UK advisory, fiduciary management and derivatives businesses of River & Mercantile.

Martin Gilbert’s AssetCo has also approached the firm.

Mr Gilbert was appointed chairman of investment firm AssetCo in March to spearhead its new acquisition strategy.

AssetCo said it has submitted a non-binding securities exchange proposal for the firm but added that any deal would be conditional on River & Mercantile completing the sale of its solutions business.

A statement from AssetCo said that RMG Asset Management and AssetCo are “highly complementary” and that a combination of AssetCo and RMG Asset Management would create significant value for the combined group's clients, portfolio managers, employees and shareholders.