The rise of 'professional' non-executive directors with higher salaries is putting their independence at risk, managers have been warned.

University College Hospital London foundation trust chair Peter Dixon warned delegates at the NHS Confederation conference that the post of non-executive director could become a 'portfolio profession'.

'The rise of the professional nonexecutive director is a problem because you are risking losing that independence - the more money you pay non-executive directors the less independent they are, ' he said.

'A non-executive director, either in a health trust or a private company, has got to walk if they cannot challenge things they know are not right.' In the future it is likely that foundation trusts will decide to increase the pay of non-executive directors above that of other acute trusts.

However, NHS Appointments Commission chair Sir William Wells said non-executive directors were now being held more accountable for the work of trusts and should therefore be paid more.

'People are starting to see the role of non-executive directors in a different way and I think That is part of the reason why the remuneration is going up, not the intrinsic need for money, ' he argued.

'They are saying: 'We have got to have some reward for the considerable responsibility we are taking on.''