Yorkshire Building Society and Norwich and Peterborough Building Society (N&P) have today merged.

N&P's members approved the change at a special general meeting in August and it was confirmed by the Financial Services Authority in September.

Iain Cornish, chief executive of the Yorkshire, said: 'From today we will be working to integrate the societies and make sure there is a seamless transition. Members using N&P's branches will still see the same name over the door and the same staff that they know and value.

'The enlarged Yorkshire will continue to be owned and run for the benefit of its members. We offer good value products, excellent customer service and the security of a strong financial organisation,' he added.

The combined society - which is known as Yorkshire Building Society - will now have 224 branches and 89 agency offices.

The Yorkshire Group, which has assets of around �33bn and 3.5m members, has said that the branch network will 'remain at the heart of the organisation' and has committed to retain all N&P's existing branches for a minimum of two years.

N&P borrowing members on N&P's standard variable rate (SVR) will immediately benefit by being transferred to the Yorkshire's lower SVR of 4.99pc based on an interest only mortgage.

This will make repayments for a member with a �100,000 mortgage, �30 lower per month. All members who were paying N&P's SVR of 5.35pc will receive a letter in November to advise them of this benefit.

The company said that by bringing the two organisations together it emphasised its position as one of the UK's strongest financial institutions.

Directors of N&P stepped down from the Society on 31 October 2011. The chief executive of the combined society will be the Yorkshire's chief executive, Iain Cornish, until 31 December 2011, when Iain leaves the society and is succeeded by Chris Pilling, who joins the Yorkshire from HSBC. The board of the Society will be the Yorkshire's Board.

The Yorkshire Group also includes the Barnsley and Chelsea Building Society brands. Yorkshire Building Society has also completed the acquisition of the Egg mortgage and savings book and the Egg brand.

The transaction comprises a �2.1bn savings book and �400m mortgage book.