If you are an employer you must offer night workers a free health assessment before they start working nights and on a regular basis while they are working nights(the Working Time Regulations 1998). In many cases it will be appropriate to do this once a year, though employers can offer a health assessment more than once a year if they feel it is necessary.
Workers do not have to take the opportunity to have a health assessment (but it must be offered by the employer).

A health assessment can be made up of two parts:

a questionnaire (which I will send to be completed pre examination)

and a medical examination (which can be performed at your premises

if you have a suitable room and more than 3 employees requiring

assessment) or can be done in one of the following locations:

Bath                                   Cheltenham              Swindon

Bristol                                Newport                     Salisbury

                                            Henley upon Thames

The health assessment takes into account the type of work that will be done and the restrictions on the worker's working time under the regulations.
If a worker suffers from problems which are caused or made worse by night work, the employer should transfer him or her to day work if possible.

Special consideration should be given to young workers' suitability for night work, taking account of their physique, maturity and experience.