Giving evidence to the House of Commons health select committee, Sir David discussed the challenge of reforming the NHS while trying to find £15-20 billion in efficiency savings.
'There is a difficult set of issues,' he told MPs. 'The scale of change is enormous - beyond anything anyone from the public or private sector has witnessed.' He added: 'People are leaving PCTs and SHAs already, and very often they are the ones we don't want to leave.'
The NHS is offering managers voluntary redundancy in a bid to cut management costs by 45 per cent. The BMA fears talented managers will leave and GP consortia will have to pay more to hire them back from the private sector.
Sir David said those who were resistant to the reforms should leave the NHS. But MP Nadine Dorries (Conservative, Mid Bedfordshire) said the redundancy scheme was a waste of money. She said: 'If it was me I'd take the money and go for a cruise because I know there will be opportunities for me when I get back.'
Sir David told the committee GP consortia would have 'rigorous' limits on how much they can spend on management.
'In the past we have let organisations decide how much they spend on administration and management. We will be very clear to them about how much they have,' he said.
He urged GPs not to discuss 'governance and organisation' of consortia, but to begin managing demand for NHS services.