Another one here who thought you were going to say 80k, absolutely unacceptable for a 35k job.
If I'm honest OP, there is no way of doing this (unless your immediate management are supportive) without getting a bit sharp, but really your end goal is leaving right? So what you can do is cover your back in terms of the law, and by that I mean evidence in case they decide to performance manage you out. Although seems unlikely if EVERYONE is overloaded, it's worth doing.
So with that in mind, here is what I would do:
- Start asking very specific questions about how long it takes your peers to complete tasks with your manager. Where is the benchmarking, how is resourcing done, how do they backfill positions - time is money, so they must know' how much time certain tasks roughly take. If they don't, you need to record how long it takes you to do tasks and then ask them to confirm IN WRITING if this is around expected levels. Then you will have a response from them IN WRITING how long they expect things to take. Then you can work on the below. They can't accuse you of not pulling your weight if they cannot get specific about expectations around time spent on the workload. It needs to be down to the TASK, not just 'get it done'. You need to ask very clearly and get a response, and if they don't give you a response in writing, you send a summary of the conversation afterwards with the SPECIFICS laid out as a 'just to confirm what we talked about' email.
- Start getting very specific about your workload and time is takes to do tasks.
So 'I have 5 x Task A this week, as well as 3 x Task B, those will all take me XXX amount of time, I also have tasks C and D to do which take XXX hours - that adds up to XXX hours which is well over my hours. Which task would you advise I pass over to a colleague or push to next week?'
Manager says 'we don't have capacity, get it done'
You say 'I have allowed for the fact that I will work XXX additional time(10% of your contracted hours, max) but that still won't cover it, what do you suggest'
Manager 'just get it done'
You: okay.
Then you send an email saying 'just to confirm, I have raised Xxx (include all the detail above) then finish with 'this will result in me working Xx hours additional, which is an additional % on top of my contracted weekly hours of xxx'
If Manager questions it, you just say 'I was just confirming what we talked about' and/or 'I'm just keeping track of my hours so that in case the opportunity to increase my hours to fulltime arises, we have evidence'
If they tell you to stop, don't. You are within your rights to send a summary of any 121 conversations. No, it's not overly friendly, but a DECENT Manager would recognise that you as an individual need to cover your back, it's not personal against them. If they aren't decent well, who cares. You won't have to put up with them forever as you are looking for a new job anyway, and they will QUICKLY realise that you are doing this to cover your back and hopefully either back off, or start writing things up themselves to counter. However, no employment tribunal is going to rule that 13 extra hours on top of part time work for 35k is in any way a reasonable expectation, despite the TOIL element.
ANY discussions on workload or performance, you write that up with detail and email it to them 'just to confirm....'
Also while you are there, start taking notes on the 'culture' - what conversations, emails do you witness where its either states or implied that the TOIL can only be taken back in form of work events etc? Again, no tribunal would deem that reasonable.
It's extra work on top of your workload, but it has the enefit of making you feel NOT CRAZY, because I worked in a place like this and you end up feeling like you are the problem. You are NOT the problem. There are PLENTY of jobs out there that wouldn't expect this, and plenty of jobs that might expect this but will at least let you take TOIL properly!! Wishing you the best.