Most contracts of employment in the UK have a line in it along the lines of:
“You should take all reasonable steps to safeguard your health and safety and that of any other person who may be affected by your actions at work. You are required to read the Company's Health and Safety at Work Rules, which will form part of your overall Terms and Conditions of Employment, and co-operate with the Company to ensure the maintenance of a safe working environment at all times.”
This is a fair statement, and one many employers use during dismissal. However, the law also protects the employee from unscrupulous employers who are not protecting their workers from harm.
Employees have the right not to be dismissed or treated unfairly because they've taken action, for example by complaining about unsafe working conditions.
A tribunal is likely to treat a dismissal as unfair if the employee (who had been employed at least two years) had been:
raising a reasonable health and safety concern with an employer;
refusing to work in situations where the employee believes they or other people are in serious danger;
completing reasonable tasks as a workplace health and safety representative, for example advising others at work not to use a piece of equipment until adequate safety measures are in place.
The Health and Safety Law What You Should Know poster, which should be displayed in all workplaces actually tells employees to do these things. If an employee is worried about their health and safety, they should “talk to your employer, supervisor, or health and safety representative.”
It goes on: “if, after talking with your employer, you are still worried, you can find the address of your local enforcing authority … via the HSE’s website.”
If you need advice on the above, speak to a HR consultant or employment lawyer, however as an employer, you should be sure of the facts and tread carefully if relieving someone from their role for health and safety reasons.