There is the school of thought that paying less gets you a more suitable calibre of person. At the end of the day, the NHS is public sector and works best in a highly collaborative manner, with the best outcomes delivered from inner passion of the employees. Paying a below par salary deters individuals motivated by money, status and competitive drive, all of which are very unhelpful motivations for those working in the NHS.
This is the same arguement being put forward to freeze, if not cut, doctors' salaries.