His attack on one of the key elements of the European Commission's proposals for block exemption beyond September 2002 comes as the SMMT reports an 18.1% year-on-year rise in new car registrations last month.
There have now been 17 months of successive growth in the new car market.
February registrations reached 93,515 units, up from 79,151 in February 2001.
Total year-to-date registrations have risen 12% to 298,991 units.
Mr Macgowan said: 'Manufacturers and franchised dealers provide the ultimate choice of models and specification by building cars to order. Any move towards supermarket style multi-franchised dealers could threaten this high level of service and open the way for salesmen to steer customers towards the brand offering the greatest commission rather than the most suitable model.'
The Retail Motor Industry Federation believes March registrations could reach record levels. Franchised dealer director Alan Pulham said: 'The high February sales figures show consumers still prefer buying from franchised dealers. We could well be heading for record sales in March.'
He put the high sales down to manufacturers upping specification levels while leaving prices stable.