Mutuals Engage Mutual and Family Investments have now rebranded as OneFamily following the completion of a merger announced at the end of 2014.
OneFamily has over £6bn of assets under management, and sells products to 1.54m Uk households, about one in twelve.
A customer benefit fund, the OneFamily Foundation has been launched with £5m over five years.
The foundation allows customers to decide how to reinvest a portion of mutual's profits provding money to members, their families and communities.
The mutual had asked advisers for feedback following the merger on its products and services.
The merger was approved by members at a vote in 2014, creating one the UK's biggest mutuals.
Simon Markey, CEO of OneFamily, said: "This is a momentous first step on our journey in creating a modern mutual - a mutual that enables families to work together to meet the financial demands of modern life."
More than two thirds of adults have supported family members financially, a survey of 2,218 UK adults conducted by YouGov for OneFamily's launch found.
The survey found that 48% were helping with day to day living costs and 21% had provided their parents with financial support.
Markey added: "It's clear that personal finance has become family finance.
"Our research tells us that families are struggling to find relevant products that meet their changing financial needs and so are turning to one another for help.
"OneFamily will look to combine our commercial success with enduring mutual values to offer a compelling combination of relevant products, excellent service and customer benefits, that genuinely put our members first."
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