Changes in how high earners are taxed will present huge challenges for attracting and rewarding talented staff, especially in the City of London, experts have warned.Both the new 50 per cent tax band – starting in April for anyone earning over £150,000 - and the bank payroll tax, which will levy 50 per cent on discretionary bonuses over £25,000, could make working in the City less attractive, said Robert Potter, chairman of the City HR Association.