"Sorry but the gents is out of order." I think would have been enough. But the note continued: "If you can't hold it, there is a pub outside the main exit". This is really handy at 9 o'clock in the morning when I took the picture. Perhaps the staff were suggesting that you could shelter by the side of the pub and have a leak.
The note ended with a cheerful "Sorry again. Have a nice day!". Really?
It's notable that there are certain parts of the system which are fairly loo-free. You're basically stuffed on the Wimbledon branch of the District Line. And not surprisingly the Misery Line lives up to its name as there appear to be very few toilets on the southern stretch of the Northern Line.
Also if Geoff's done his research correctly it looks like if all the toilets are working, us girls should have a better time of it. Turnham Green, Baron's Court, Amersham & Highgate all have a Ladies' loos and no Gents. Whereas only Mill Hill East and Upney have Gents but no Ladies. Guys, I think you should campaign for the balance to be re-dressed!