the LAW on fitting slam locks to a vans front doors

i know its ok for the rear and side doors, but for the 2 front doors is it illeagle as im sure i have read it is. The only reason for this if i remember correctly is in the case of an accident and the driver is knocked unconsious and no one can get in to help??

Can any one help me in this matter or point me in the right direction

cheers Andy