The UK’s third biggest building society has announced plans to merge with a smaller rival in a series of tie-ups, which will create a number of joint branches in the West Midlands.

Coventry Building Society has agreed a deal with the Stroud & Swindon Building Society, the UK’s 11th largest mutual, that will create a combined group with around 1.5 million members and assets of around £21.1 billion.

The enlarged business will have a combined network of 91 branches and agencies across the Midlands and South West.

The firms said no branches or agencies will be closed as a result of the merger and all Stroud & Swindon staff from these parts of the business will be retained.

But a number of jobs at Stroud & Swindon’s head office could be at risk as operations will be transferred to Coventry over an 18-month period.

Stroud & Swindon employs 215 people at its Stroud head office and said some staff could relocate to take up an extra 100 positions in Coventry.

The combined organisation is to be called Coventry Building Society and based at the larger firm’s headquarters. There will be no bonus payments made to members of either institution on completion of the merger.

Coventry chief executive David Stewart said: “Coventry’s performance over the last three years has demonstrated the strength of our traditional building society model.

“I believe that the merger with Stroud & Swindon Building Society will help us build on recent successes and bring the benefits of our prudent and member-focussed approach to a wider membership.”

The mutual has weathered the economic storm well and saw pre-tax profits more than double to £56.2 million in 2009. It has 48 branches throughout the Midlands and 1.2 million members.