They will need planning permission for the unit to be used for business purposes. Talking to your council may get them to be more considerate in their overspill into the local roads. THey have a duty of care for their customers property as well so the customers might be unhappy about the security of their cars. Ask advice from the Fire Brigade about obstruction, they may choose to engage the business and remind them of the fact that they are permitted to smash windows on cars if the are an obstruction to hydrants etc.