Dubtrub... quite a few units in the UK monitor more than one frequency. For example, almost all Military a/f use UHF and VHF (although the callsign will in most cases betray to an alert controller whether you are calling on V or U)...
Then you have "band-boxing" the practice where one controller is providing two control functions during of peak-times, and therefore monitoring two different frequencies. Once again the nature of your request might give an indication as to which freq you are calling on, but it is surely simpler not to second guess what the guy on the ground is doing when you don't (apparently) understand?