I didn’t know about this legislation so thought I’d share. If you think your employer has not taken appropriate measures to protect you but says you should go back, it should protect you from risk of harm:
Section 44 of the Employment Rights Act 1996
Legislation text:
www.legislation.gov.uk/ukpga/1996/18/section/44
Interpretation help (just one of many on the web):
section44.co.uk/