British insurers CGU and Norwich Union are expected to announce today that they have agreed on a merger to create an insurance giant valued at $30.5 billion, industry sources said. After weeks of secret talks, CGU and Norwich Union had agreed on an all-share merger of equals that would create a British powerhouse ranking first in general insurance and second in life and pensions behind Prudential Corp., the sources said. They said that with premium income of more than $40 billion and more than $305 billion of funds under management, the new titan would rank among Europe's top five insurers. Norwich Union would not confirm nor deny the deal but said it would make a statement today. It is expected to be structured as a CGU takeover of Norwich Union.