Section 3.1 of the 1974 Health and Safety at Work Act.....
"It shall be the duty of every employer to conduct his undertaking in such a way as to ensure, so far as is reasonably practicable, that persons not in his employment who may be affected thereby are not thereby exposed to risks to their health or safety".
http://www.legislation.gov.uk/ukpga/1974/37/section/3
If they had a duty of care and if section 3.1 has been breached and can be proven to be breached then you have a case.