No, Police Officers don't have the same rights as everyone else in the UK when it comes to employment law.
There are restrictions which (possibly) didn't exist when he joined, and one of those is that if you have been served with a 163, a formal notice of investigation into disciplinary or criminal matters, you can be prevented from resigning, or retiring.
The IPCC had already served him with that formal notice once, and then I understand, with a subsequent form saying that no further action would be taken. As the result of the Inquest, they have now decided to have another bite at the cherry. No doubt if they don't find a reason to hang the officers concerned this time, they will try again, and again and again in the usual IPCC desperate attempts to get a Police Officers found guilty. The simple fact is that the IPCC is as independent as attilla the hun!
As they have not served him with a new 163, he should be free to leave if he wishes. The IPCC just want to have a body to show.
This is an utter waste of public money. The CPS have already binned any idea of criminal proceedings, so the most that can happen is a Kangaroo Court Marshal, which has resemblance to a Blackadder episode, where Gen. Melchett gives the order "March in the Guilty Bas......" and follows that by asking where the Black cap is, as he will need it. No evidence of course having been heard. And indeed the only evidence that will be taken any notice of in any Disciplinary hearing will be that against the officer, however dubious it is.
The most that can happen, is the officer gets sacked, pointless considering he wants to resign! Letting him stay of course means that we the tax payers will have to pay him for that time, and the IPCC are not known for being quick, efficient or very good at investigating things. As for his pension, it remains, it can't be stripped from him unless there are very good grounds. It has only happened a few times since that option was given to Police Authorities (Now PCC's), and would doubtless be challenged by the Federation if that was tried.