The Health and Safety at Work Act 1974 says that –
IT SHALL BE THE DUTY OF EVERY EMPLOYER –
TO ENSURE, SO FAR AS IS REASONABLY PRACTICABLE, THE HEALTH SAFETY AND WELFARE AT WORK OF ALL HIS EMPLOYEES.

(This duty extends to ALL employees including those that are employed by a contract of employment or service)

To provide and maintain:

• (a) Safe plant and systems of work
• (b) Safe articles and substances
• (c) Information, training and supervision
• (d) Safe place of work
• (e) Safe environment & welfare facilities
  “so far as is reasonably practicable” (Section 2 HASAWA)

also

IT SHALL BE THE DUTY OF EVERY EMPLOYEE –

To take reasonable care for the health and safety of himself and of other persons who may be affected by his acts or omissions at work.
and
As regards any duty or requirement imposed on his employer or any other person by or under any relevant statutory provisions, to co-operate with him so far as is necessary to enable that duty or requirement to be performed or complied with.

Did you also know that –

HASAWA Section 40 says that

The Onus of Proof is such that it is up to the employer to prove that they did what was reasonably practicable