Shell have a look at this link about rules employers have to comply to:
www.gov.uk/working-when-pregnant-your-rights
"Health and safety for pregnant employees
When the employee tells her employer she’s pregnant, the employer should assess the risks to the woman and her baby.
Risks could be caused by:
heavy lifting or carrying
standing or sitting for long periods without adequate breaks
exposure to toxic substances
long working hours
Where there are risks, the employer should take reasonable steps to remove them, eg by offering the employee different work or changing their hours.
The employer should suspend the employee on full pay if they can’t remove any risks, eg by offering suitable alternative work.
For full details about the regulations see the Health and Safety Executive website.
Pregnant employees who think they’re at risk but their employer disagrees should talk to their health and safety or trade union representative. If your employer still refuses to do anything, talk to your doctor or contact the Health and Safety Executive.'
Do you have a union rep? Perhaps you could speak to citizens advice.