The architect of Operation Breakthrough, a system of funding large contracts for housing associations, as hit back at house builder critics of the scheme.Sir Norman Wakefield, deputy chairman of the Housing Corporation and former head of Lovell, complained of the 'conservative' building industry which he once championed.He was responding directly to House-Builders Federation director Roger Humber who said volume bids - where a contractor or developer works with one or more associations on a number of sites over period of time - could be a 'con'.Sir Norman chose the annual meeting of an association involved in the biggest volume deal struck so far to reveal that the corporation was looking at ways of extending the volume bidding system.He also revealed top-level concern about the viability of some companies which might be building 'relatively large programmes.'He was speaking at the annual meeting of Hexagon Housing Association, one of three associations involved in the £90 million South Thames Housing Partnership.He said: 'There must have been many times when you wondered if the industry was not structured to deliver what you were looking for.'We do not seem to have convinced or won over a traditionally conservative industry.'Apart from a handful of innovative companies, much of their knowledge remains as yet untapped. It seems incredible with market conditions as they are, but contractor attitudes die hard.'Sir Norman said he had expected contractors and developers to set the pace in setting up volume deals 'but now I conclude it will have to be the (housing association) movement.'