BBK, operating a Heavy out of LHR you should be aware that you can go 'wheels up', as we call it, behind any other Heavy....if you're all lined up ready to go, this can be as little as 45 seconds.
If you don't want this, then please advise TWR when in the holding area that you require 2 minutes (or whatever you need) behind a certain type....providing that you tell us before you enter the runway, we can work around it.
The worst thing for us is to have someone on the runway cleared for take off and then tell us that they need another minute due to wake turbulence.