I'm sure most of the people that work in the tower at EGLL would agree that if we use "give way to...." we would expect you to hold and wait until the other aircraft has passed. After all, you are in Class A airspace, and the ANO states that you will "Comply with ATC instructions at all times". Come to think of it, that applies to Class D as well.
What you have to bear in mind, is that a lot of controllers nowadays are extremely busy when doing GMC and there is a very strong tendency to file 1261s at the drop of a hat. Please don't become the "accused" by trying to be a smartass and cutting somebody up against contrary instructions. Paperwork is very time consuming and not a lot of fun for anybody involved
The other option of course, is to make the effort to visit the VCR at a unit and find out just how busy the GMC controller is, then maybe you will think twice before trying to be too clever!!