Was a proper record made of the injury at work? That is a legal requirement the employer must abide by.
If you are told not to do it when H&S are there then you do have the basis for a claim for loss of earnings, pain and suffering, loss of enjoyment of your normal activities.
You have 3 years to make a claim so there is no need to be hasty - far better to take your time and make sure everything is in place before you consult a solicitor or your union rep.
Take photos of your injuries - and the scene. If no photos were taken at the time maybe a colleague could take photos for you. These should show the machine, the slats and if possible people walking on them (the faces can be blurred).
Keep a detailed record of everything - hospital appointments, doctors appointments, prescriptions, the progress of your injury including pain levels. Also, every penny you spend on travel to the appointments, prescriptions and everything else connected to the incident. Record everything you have been unable to do because of the accident. Have you had to cancel social events, ask for help for day to day tasks?