Speaking on Radio 4's Today programme, Mr Pattison said that valuers were given a very restrictive brief. The whole job had to be done in six months and valuers were not allowed to gone into private constraints upon it.
'The government wanted a rush job done at a low cost - it got that and now there is some tidying up to do at the margin,' he said.
Mr Pattison thought the figure of two million incorrect valuations estimated by the NAO was too high. A better measure was that there were 900,000 appeals now in the system.