The Clydesdale and Yorkshire banks are to cut more than 1,400 jobs in the UK by 2015 because of the "deterioration in the economic and operating conditions".
The banks' owner, National Australia Bank (NAB), said it made the decision following a strategic review which was announced in February.
Clydesdale and Yorkshire will now focus primarily on Scotland and northern England as it closes 29 of its financial solution centres in southern England, as well as six back-office locations.
NAB said the review was in response to "the deterioration in the economic and operating conditions" in the UK, particularly in the commercial property market.
Clydesdale and Yorkshire banks racked up a £25m loss in the first half of the year, compared with a £77m profit in the previous year, reflecting a higher charge on bad debts and higher funding costs.
NAB chief executive Cameron Clyne said: "In the last half-year there has been a significant downgrade in the growth prospects of the UK economy, in part reflecting the drag on its recovery from heightened weakness in the eurozone.
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"The action we are taking is needed to adapt to this current economic environment in the UK, and to reposition the UK banking business to improve returns for the group over the medium term."
He added: "While every effort will be made to support our people, the substantive repositioning of the business will impact roles in the UK."
Yorkshire Bank was founded in 1859 in Halifax, West Yorkshire, and has 185 retail branches, while Glasgow-based Clydesdale, which was bought by NAB in 1987, has 152 outlets.
Following consultation, the UK's workforce will be reduced to around 6,900.
NAB has been the subject of deal speculation over the last year after it was unsuccessful in the auction of 318 branches put up for sale by Royal Bank of Scotland, a deal later secured by Spanish giant Santander.