copyright law states: http://www.copyrightservice.co.uk/copyright/p01_uk_copyright_law
It is an offence to perform any of the following acts without the consent of the owner:
> - Rent, lend or issue copies of the work to the public.
It is advised not to not 'rent' anything that has not been purchased as a 'rentable' asset with regard to copyright. Even lending for free - with a subscription model - could still be deemed "renting" regardless of whether DVDs are second hand.