you might be talking to farnborough
The thing that always annoys me is when someone is talking to a FIS of some sort, outside controlled airspace, and then "requests" to leave the frequency. What is the controller going to do? Refuse your request because he's got nobody else to talk to? You didn't have to speak to him in the first place so it's completely within your right to terminate the conversation.
Your message should be along the lines of "I'm going to leave now, thanks for the help, see you next time." No request in there. (Although you will have to put it in some sort of ICAO format though: "G-XX leaving the frequency, bye-bye")
(Edited to say that you are required to sign off with them, due to the alerting service that's implicit in a FIS. You cannot simply leave the frequency without telling them.)