From Wikipedia and
http://www.martinsbank.co.uk/11-36-00%20Bangor.htmMartin's Bank (with an apostrophe) was a London private bank, trading for much of its time under the name of “The Grasshopper”, that could trace its origins back to the London goldsmiths. Martins agreed to its acquisition by the Bank of Liverpool in 1918. The Bank of Liverpool wanted Martins to give it a London presence and a seat on the London Clearing House; the Martins name was retained in the title of the enlarged bank which was known as The Bank of Liverpool and Martin's Limited. The title was shortened to Martins Bank Limited (without an apostrophe) in 1928 at the insistence of the directors of the Lancashire and Yorkshire Bank when it merged with the Bank of Liverpool and Martins. The Head Office and managerial control remained firmly in Liverpool, cementing Martins' place as the only British national bank to have its Head Office outside London[1]
The Bangor Branch opens in 1963, at a time when Martins’ expansion into the south, east and west of england and Wales is gathering pace.The bank was bought by Barclays Bank in 1969, when all of its 700 branches became branches of Barclays.