The Co-op Bank launched the residential mortgage-backed securities deal last week under its Silk Road Finance programme, and is due to close at the end of February.
A spokesman for Britannia, which merged with The Co-operative Financial Services last August, says that initial feedback to the issue has been good.
The Co-operative Financial Services is part of The Co-operative Group and is made up of The Co-operative Insurance and The Co-op Bank, which includes the internet bank Smile and Britannia.
It follows another RMBS deal from Lloyds Banking Group, also worth £2.5bn, at the end of January.
The Lloyds issue, the second from its Permanent programme in the space of four months, offered assets in pounds, euros and more unusually US dollars and reported a good take-up from US investors.