Contact CAB, they’ll recommend you to an Industrial Solicitor if they think there is a case to answer, were you signed off at the time, was it due to workload etc etc your problem came on.
Don’t put it off though, get the boring CAB stuff done now – THEN ride your bike.
Something better will come along, did for me, left absolute sh*thole, went to work in a warehouse and ended in a job where I spend most my time answering to myself on here. :-)