Asda is investing £30m in facilities for people with disabilities between now and October 2004.
The retailer has also recruited disabled mystery shoppers to check out all its 260 stores four times a year.
The programme, dubbed Mystery Shopper Miles Ahead, has been trialled over the last four months and stores have scored 70% or more from shoppers, said an Asda spokesman.
People who have mobility difficulties look at disabled parking, the hard of hearing check out induction loops, while the visually impaired assess how clutter-free aisles are.
Staff friendliness and the ease with which they interact with a disabled shopper is assessed from when the shopper arrives in the car park.
Staff are marked down for inappropriate expressions or behaviour that the shopper believes is provoked by their disability.
The £30m will be spent on facilities including induction loops, tactile signage, lowered counters for wheelchair users, and mobility aids in stores and depots. Elevators have also been revamped for ease of use by people with disabilities.
The expenditure should ensure Asda premises are compliant with the 1995 Disability Discrimination Act designed to give equal access to public premises and services by October 2004.
Asda customer services director John Irwin said: "The mystery shopper scheme will ensure that wherever you shop, facilities and customer service provided in Asda will be of a consistently high standard."