As an electrician I was told I must do the mechanics job, it was in my contract I have to do any job my foreman says I should do, clearly designed so I can't refuse to brush up when no other work available, which I suppose is fair enough, however it all went wrong, and it cost the company around £500,000 as a result in sickness benefit and compensation and legal fees, likely more as the foreman was asked to resign and he also put in a claim.
As to if I should have refused a second time after told to do the job, yes in hind sight I should have done, as I never worked again. But that is hind sight, and easy to say after the event, to have helped the mechanic would have been OK, to do his job without him checking the method statement and completing the risk assessment was however wrong.
As to if you can refuse is another question, it was accepted by the legal department that having refused once, the foreman should not have forced the issue, but had it gone the other way, and I had not done the job, and as a result was let go, would the courts have found in my favour then?
Even as a qualified electrician where I volunteer now, I am not permitted to do electrical work.