The Health and Safety Executive outlines that employers have a general duty under section 2 of the Health and Safety at Work etc Act 1974 to ensure, so far as is reasonably practicable, the health, safety and welfare of their employees at work.
The Health and Safety at work Regulations 1999 further details these responsibilities outlining that employers must risk assess for all new and pregnant employees as well as regularly reviewing the risk to the current employees.
The HSE advises that employers should look at:the whole workstation, including equipment, furniture, and work conditions
the job an employee is doing
any special requirements of a member of staff, for example a user with back pain
Where there are risks, the employer should take steps to reduce them.
Employers must also do an assessment when:
a new workstation is set up (this is particularly relevant with employees now more readily working at home, both the desk space at work and home require assessment)
a new employee starts
a change is made to an existing workstation or the way it's used/job role has changed
an employee complains of pain or discomfort
https://www.hse.gov.uk/msd/dse/assessment.htm#article