Work stress
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I don’t have any advice sadly but I work in HR and we have no real influence on salaries it all comes from management so your line manager is probably a better person to speak to. You can ask HR for a stress assessment, or further support in your role. Good luck x
I think you articulated it really well actually - would rather take the 29p pay cut and less stress! Emphasise that you have to put yourself first at this stage of your life and ultimately you feel unsupported and undervalued. You do x y z in your role and it results in X y z for you and if you took a 29p paycut you could have much less stress and not that much impact to your income. Would only suggest that route if you really can afford to take the paycut and you'd legit be willing to do so because they may call your bluff a bit!
HR cares more about the company than you unfortunately and this seems more like you should speak to someone in management. I don’t think HR has anything to do with salary/wages
Do you have a written job description that you can reference and say "this task is not in my job description"? Or find other job listing's for the same position that pay better so you can show them that you deserve more pay. They're not likely to say "sure we'll take work off your plate" because that would require them hiring someone else and paying them and clearly they don't want to pay more so you'll have to either prove why you deserve more money or be willing to say you'll leave if the workload and pay are not leveled out. But don't threaten to leave if you're not actually in a position to do so. Honestly these conversations go better if you have another job offer in hand so they take you seriously