This is spousal rape. Forced sex is rape. Rape in a marriage is spousal rape. As far as definitions go, it really is clear-cut. Regrettably, recovery isn't.

As far as involving the police goes.. The police SHOULD take you seriously, but there's no certainty that they WILL. I think you should ask yourself whether it's worth the risk of how you will feel if you're waved off or ignored. That's a decision only you can make - however, a therapist can assist you with that.

In my country, there's an option that you go to the police to file a report, but they don't make it an 'accusation'. So basically they'll put into your report into the system, but they won't follow up on it until you make it a "formal accusation". Maybe something similar exists in the UK. That way you could make your report, but there is less chance of being waved off because you aren't asking them to follow up on it anyway, and it would give you some time to decide whether you really want the police to investigate. But if you decide in two years you want the police to investigate, they will process the old report: and the date will show that you reported it reasonably short after the incident, and not years later.