Amber River said the asset manager will also continue to work with adviser businesses outside of the group post-acquisition.
The acquisition is part of Amber River's strategy to expand its solutions for advisers and their clients, the firm said.
TAM has just under £650m in assets under management and, under the M&A deal, its range of low-cost portfolios will be made available to the wider Amber River Group alongside the company's existing investment solutions currently used by its 13 regional hubs.
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Amber River said the asset manager will also continue to work with adviser businesses outside of the group following the acquisition.
Amber River founder and CEO Mary-Anne McIntyre said: «Lester and his team have built a dynamic, forward-thinking business with the sort of ambitious and entrepreneurial spirit we value highly at Amber River.
»Having them as a centre of investment excellence in the group is an important and exciting development, and, alongside market-leading mortgage specialists Charles Cameron, further extends our customer proposition, professionalism, and strategic resilience."
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Lester Petch, CEO of TAM Asset Management, added: «The deal with Amber River is a natural next step for the business and our clients and one we are extremely excited about. As a team we believe passionately that everyone should have access to expertly run model portfolios regardless of wealth.
»Having the backing and support of Amber River will be a major boost to helping us achieve this, enabling us to further increase awareness and understanding of our innovative, low-cost investment solutions with advisers
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