Some background knowledge to help you all understand why it WILL be 18,000ft (and why it is also DIFFERENT from the USA & Canada)
The powers that be have decided that Europe will harmonise their TA's. 18,000ft was decided as it clears every European peak by at least 1000ft other than a couple that lie on the edge of European airspace in Georgia and Russia. NATS (UK) Airspace will not be initially redesigned but some minor changes will occur, including the removal of FL190 for any use, but the long term picture will involve major redesigning. Not all of Europe will make the change at the same time so NATS are working on the best way to accept/handover aircraft at the boundaries.
The main reason for this need to change is all about the environment. Some study has highlighted just how much extra fuel is being unnecessarily burnt by departing flights due to our airspace structure and TA. With the London TA set at 6000ft, that is the maximum level that any SID can finish at, as a SID cannot use flight levels. If aircraft could get airborne and climb straight to 10000ft or even higher as stated in the SID (even with steps built in), then they could carry less fuel (rather than planning to stay at 6000ft under all the stacks at LHR say). Carrying less fuel obviously has many advantages for the entirety of the flight in all phases. This will mean moving the stacks and conducting holding at higher levels (another fuel saver too), and will combine with the other projects including passing EAT's up to an hour in advance and losing time enroute to avoid excessive holding.
This TA is different from what is used to the West of the Atlantic, as my understanding is that the TA over there is actually
FL180, the last altitude is 17,999ft. We will use
altitude 18,000ft and the next
recognised flight level will be FL190, although this probably will never be used!! It is just because we have to be different and those that don't use, never understand.