Ok, to clear up a few bits then!
The last altitude in reference to altitude in America is 17,999ft. The first recognised flight level is FL180, as Airbubba clarifies above. I wrongly worded that then, but you got the idea.
So SID's can finish at a flight level as proven. I will check this out but looking further into this, it looks like safety have intervened regarding stepped SID's in the London TMA. Having a transition in the middle can lead to someone getting it wrong or more so, when EXACTLY do you select 1013hpa? Think Zooker's drift below shows kind of an example of that, but if we modify it slightly and say the aircraft holding was kept at FL70 so the departure could safely go underneath, what happens if the departure levels at 6,000ft THEN selects 1013hpa to find they are now a few feet closer as a result? As I said, I will check this out further.
Defruiter:
I heard that the French and Germans have said no to it, so it kind of defies the purpose really...
Don't know where you heard that, the French have been involved in the consultation and when asked, also suggested 18,000ft. They did say they would be unlikely to change at the same time as the UK, but that they supported the change. Don't know anything about the Germans.
Not saying I am pro this or anti it, I see arguments from both sides of the fence with equal force, but with the Euro Union on their pro-Eco drive, thats why I say it WILL happen as it isn't just a NATS idea trying to be shoe horned in.