Australia's fourth biggest bank announced the restructuring alongside a 15.6pc fall in first-half net profits fell to A$2.05bn (£1.32bn) in the six months to March 31.
The results follow £456m of writedowns and restructuring charges at its UK division worth, including £120m set aside to cover mis-sold payment protection insurance.
NAB said it had completed a strategic review of its British assets to adapt to weak economic conditions, with the business to be simplified to focus on retail and small business lending in Scotland and northern England.
It plans to close 29 of the banks' 73 Financial Solution Centres, which offer services to businesses and better-off individual investors, and merge nine others with local retail branches, adding that the changes would mainly affect operations in the south of England.
Six back office locations would also shut.
Cameron Clyne, the chief executive, said the review was undertaken because recovery in the region was now considered a longer-term prospect.
"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," he said.
"In addition, the commercial property market, which had previously seen signs of recovery, has recently experienced a 'double dip' as the recovery stalls and other banks accelerate the reduction in their commercial real estate exposures.
"This has contributed to the current downturn in the UK being longer and slower to recover than experienced in the 1930s following the Great Depression, and has led us to take these actions at this time."
NAB will also take on most of the unit's commercial real estate exposure of £6.2bn. The transferred commercial real estate portfolio will be run off as the assets reach maturity.
The bank said the changes would cut the UK unit's reliance on wholesale funding that had become expensive after credit rating downgrades, move the business to a more deposit-funded base and reduce group funding support to the UK unit by £5bn.
The Australian bank said an immediate sale of the UK unit was ruled out because it would fetch less than book value.
NAB bought Clydesdale Bank in 1987, followed by Yorkshire Bank in 1990. Between them they have around 330 branches.