They’ve written to the company’s board after stories broke of a rival challenge from Swiss entrepreneur Marco Garzetti.

Mr Garzetti said he would do “whatever it takes” to keep the Swiss fund management group independent in an open letter to GAM shareholders on Friday.

GAM fund managers have responded with their own letter sent yesterday to the company’s board of directors.

In it they said they strongly support the decision by the board to recommend the offer from Liontrust for all shares in GAM on the basis that they believe this to be in the best interests of GAM clients.

The senior portfolio managers wrote that “it is our view that an industry sale to a highly regarded peer with a heritage in fund management, a strong track record of acquisitions and integrations and consistently strong profitability is in the best interests of GAM clients.”

“We believe there is a cultural alignment between GAM and Liontrust, and this will provide the environment and support to enable the investment teams to focus on their clients’ best interests.”

“Liontrust has a clear vision for the future, with a focus on investment and wealth management only, and an impressive strategy for how to grow the enlarged company. This strategy importantly includes a commitment to developing the business in Switzerland and GAM’s global presence.”

The Swiss firm agreed to be taken over by British rival Liontrust earlier this month in an estimated £96m deal, with the acquisition expected to complete in the final quarter of this year.

GAM has had a turbulent few years, hit by a falling share price and customer outflows.

It is headquartered in Zurich, employs 594 people in 14 countries and has UK investment centres in London and Cambridge.

Liontrust plans to merge the investment management businesses which will have 12 funds with assets more than £1bn (seven managed by Liontrust and five by GAM).

The fund manager intends to rebrand all GAM funds as Liontrust.