You should ask the safety committee or a safety representative to report your employer to the relevant regulatory authority. In most cases, this will be either the Health and Safety Executive (HSE) or the local authority. HSE inspectors have the power to:
inspect and investigate;
take measurements, samples and photographs;
require an area or machine to be left undisturbed;
seize, render harmless or destroy dangerous items; and
obtain information and take statements.
They also have the power to issue improvement and prohibition notices, and can bring prosecutions against any person contravening a relevant statutory provision.
The HSE has produced a useful list of the enforcing authorities for different sectors.
In very serious situations, where you face a serious and imminent danger to your safety, the law gives employees the right to leave their workplace until the danger has lifted. Employees must not be penalised for taking this step. Agency workers probably don’t have this statutory right.
There is information on the main TUC website about this right in the context of the coronavirus pandemic. The TUC highlights that the first thing you should do if you are worried about safety at work is to talk to your workmates and your union. You should ask your employer to rectify the issues you’re worried about. You can read the rest of the guidance here.
It is very important to take advice from your union before taking this step and also that you act together with your fellow employees, making your demand for a safe workplace a collective rather than an individual one. Unions stand up for the workers in times of trouble, so join a union.