The shock bank tax announced in the UK budget this week will complicate National Australia Bank's sale of Clydesdale Bank, says Commonwealth Bank of Australia analyst Victor German, who has sliced his valuation of NAB's difficult UK asset by $425 million. UK chancellor George Osborne surprised the market when he announced an 8 per cent tax on bank profits in the UK budget on Wednesday, which also removed a controversial bank levy that HSBC and Standard Chartered had argued could force them out of the UK.