Atc Plan
On the NAT PCO site is access to MNPSA which is the bible on all the requirements. Very last annex 4 has everything required on the plan.
In the body of the flight planning section (4.1) is a link to a site which has this info, plus sample plans. (in the flight planning section) I tried copying the link but when transferred to here it doesnt work.
It is a yellow circular UK AIC 55/2003.