Additional/spare card

I just thought it would have been useful to have an additional/spare card with a spending limit in order to give it to family/friends (e.g. to use as an oyster card when family members visit, for convenience of friends who visit from abroad, to give to the family members when they need extra cash or to make a purchase). I guess it’s difficult legally, but if it’s registered on my name and I take responsibility for its usage, there shouldn’t be a problem.