On What Evidence?

I know nothing of the specifics of the case, but it's possible that the police had evidence against him that proved he was a rapist, but was inadmissible in court for technical reasons, leading them to believe that a conviction would not be possible.

If inadmissable, that brings us right back to the employment tribunal - admit it or re-employ him. This tale twists no matter how it's looked at....

It's a punishable (I dont know about sackable) offence even if the sex was consentual. I understand what you're saying about inadmissable evidence that means the court case didn't hold against him, but if the entire MET knew he was guilty then his position would be untennable

My understanding is officers usually aren't sacked for sex on duty/on police property/etc. However, I won't pretend it's an area of expertise for me.

Untennable-position wise, you make a good point.