jackharpenden
I haven't worked in EINN for a couple of years, but Ill give this a go.
Firstly, the clearance that you have organised from Shanwick for crossing the NAT is an Oceanic clearance (Which Shanwick controls)....it is NOT a clearance for Shannon ATC airspace.
This clearance (and any amendments) will be electronically sent by the Shanwick controller to the Shannon controller.
He/she will then start planning to have you at the level, at the cleared Mach number, at the NAT entry point, within 2 minutes of the time that you are cleared to enter.
You should NEVER begin a climb/descent without a clearance from the controller that is controlling the airspace that you are currently in.
Regarding the flight planned climb...why wouldn't an aircraft request a climb in the Oceanic airspace?...its just like any other airspace, the level will be either available, or not.
Having said that, looking at that plan, it looks like that is his requested entry level and Mach number into the NAT.
cheers