I work part time in sales in the UK. 31 hours a week (my wife works nights so I have to be there for childcare) and generally these are the hours I do although sometimes to help out with annual leave, I have done extra at my normal hourly rate. About 80% of the work is office based but there is a trade counter so 20% of my time is face to face interaction with members of the public.
Later this month, 3 of the senior managers in the company are taking holiday at the same time. My sales manager and both of the guys who usually sub in when he takes annual leave. This, along with the fallout from Covid and maternity leave means that I will be left alone in the office, doing the job of between 3 and 4 people.
In addition to this, I suffer from anxiety and depression, well known by the company and I have semi-regular chats with HR about it. In my most recent meeting, I was asked how the company could help and I requested a stainless steel table so I don't have to have direct contact with customers. If they've bought something in with a "I want one of these" or handing them their goods, I could use the table instead and keep my distance. That was 3 weeks ago and there's no sign of a table or my anxiety diminishing.
I don't ask for much and have taken the lack of a table as a sign the company really doesn't care about me (not like I hadn't really worked that out anyway) and really aren't sure I want to do the extra hours. In truth, I was asked if I could do the extra and when I said I could do, it was just assumed that I would do it although no one has ever explicitly asked me.
I'm very tempted to say to them that I'll do my contracted 31 hours and keep my mental health intact unless they're willing to be generous in terms of an overtime rate but not sure this would fly since if I can do the hours, the company will assume I can survive it at my normal rate.
So, great people of stack exchange, what would be the best way to negotiate an enhanced rate for the extra 14 hours I'll be doing?