If a family member is shopping for the card holder, and the card holder is either not accompanying the driver or is sitting in the car, the blue badge must not be used, nor a disabled parking space.
These can only be used by the disabled badge holder.
The confusion arises because of the 'disabled class' road tax, which is free. The vehicle can only be used by the disabled person, or on behalf of the disabled person, so somebody else could drive it to get the disabled person's shopping, without the disabled person.
It is an offence if people other than the badge holder take advantage of the parking concessions provided under the scheme. The maximum fine if someone is convicted is �1,000 plus any additional penalty for the related parking offence.
If you are a badge holder, it can only be used for your benefit. If a trip is for someone else and you are a passenger and staying in the vehicle, you cannot use the badge simply to let them benefit from free parking.
http://www.direct.gov.uk/en/DisabledPeople/Mot oringAndTransport/DG_4001061