It's the last thing we need on already congested TMA frequencies. Whatever the hell was wrong with "Climb now"?
The amount of scenarios where climb is required immediately on instruction far outnumbers the amount of times where the SID profile needs to be followed. In fact, I cannot think of one occasion where an aircraft following the vertical profile of the SID on climb above the SID level would have been of any benefit at all. There is no guaranteed separation above SID levels.
If this instruction is to be followed on a London TMA departures sector at peak traffic, almost every aircraft is going to have to be given this instruction. Even now in our supposed quiet period I sometimes find it difficult to get in on the RT. What's it going to be like with summer traffic levels?
I'll not be using this new phraseology any time soon unless it causes confusion. A simple "Climb now" (with emphasis on the "now") will suffice. It's much safer and a lot more efficient.