PIP Free Road Tax Rules

Largely thanks to the help of this excellent Forum I have been awarded Enhanced PIP Mobility entitling me to free road tax - which I have applied for by signing the V5C and handing it in at the Post Office to get the vehicle taxation class changed to Disabled.
Friends drive my vehicle (disability adapted LGV van) to ferry me about and get my shopping etc which I believe is still allowed.
But what if they need to drive my Disabled taxed vehicle for a journey for their own use – is that allowed under the rules for my free road tax?
In the circumstances (their helping me so much) I really don’t want to have to say no – I would rather pay the road tax and keep it as LGV – so I can help my friends out by lending them my vehicle when I don’t need it in return for their helping me.
In which case can I stop the process of it being changed from LGV to Disabled tax class?

James

The Gov.UK website says that the car must only be used for the benefit of the claimant, I don't know what that means in practical terms but most insurance policies state that if the car is not properly taxed then the cover is invalidated.

Gordon