I believe you can get mobility allowances to cover taxi for shopping 
It's good for the elderly to get out if you can  
If you open an asda account shopping on line is ok , you will be charged, but if you consider the travailing costs you would have to pay your self, its not that expensive 
Stock up big on the non perishables basic's and you can cut down on the frequency of shopping.
Age concern can give advice on these issues and more 
http://www.ageuk.org.uk/about-us/