Hmm, in order for it to be a brothel, there would have to be someone else offering sex at the same premises. There's something someone's not saying.

Having 'seventy police officers' raid the 'flat' is odd too.

The police in the London borough of the project I used to work at had a target of raiding about four brothels a year. There were more than that on the street we were based on! None of them were particularly secret and another brothel in the borough had been on the front page of The Sun for two days - it was where an MP met his boyfriend. The choice as to which they'd go after wasn't taken lightly and they'd make sure they knew what they'd find before they went through the door.

My guess would be he was being investigated for something far more serious -  those seventy police! - and this is all they could find. But again something's very odd about this. If he has even vaguely competent lawyers, they will have said 'where's the proof someone else was offering sex there?' months ago.

(Oh, as well as the brothel offences, the other surviving bit of the Sexual Offences Act 1956 is an offence of allowing habitual prostitution in somewhere that's not yours, but as far as I can see, no-one's been prosecuted for that in decades.)