Steve Hughes, chief executive of Coventry Building Society, described it as an exciting moment.
“We’ve spent a lot of time evaluating this opportunity and believe it’s the right thing to do,” he said in a letter to customers.
The lenders said they were working together to firm up the arrangements of the deal and stressed there can be no certainty that an acquisition will happen.
The two firms will retain their current names and branding while they work to finalise the deal.
Co-op Bank has 50 branches across the UK with about 3,400 staff. In March, it said it was planning to cut about 400 jobs as part of efforts to cut costs.
