The situation we have in the UK is that we take up rule changes from the European Community and US and enforce them totally, whilst other the other countries involved appear to apply a slack interpretation.
Before this thread goes off an a tangent and before a list of "my favourite jumpseat rides" are collated, I think a little direction is required:
Within the UK, the
dti enforced the present rules, which are not at the behest of the EU, but have been brought in due to advice from security experts within the government. This applies only to UK carriers, and was applied not following 9/11, but in
Summer 2002. After such time there should be nobody whatsoever in the flight deck on any UK-registered aircraft. No amount of paperwork and pre-planning will enable anyone to travel on the jumpseat. The only people whom belong there have very good reasons to be there, sanctioned by management and operating crews.
European carriers can do whatever they want according to the rules of their country of registration - although the UK prefers that nobody be in the flightdeck within UK airspace, other carriers can and will do what they want within their own countries' rules.
Flights to the US on any carrier are however prevented from having anyone in the flightdeck at any stage by US authorities. US carriers have similar rules to British carriers outside of US airspace as well.
It is not complex - just don't bother asking and embarassing anyone if you are on a UK or US carrier or travelling to the US. If of course you have been in a jumpseat after Summer 2002, you would be advised not to post in the public domain, and consider that if you know the rules and are a party to breaking them, that if found out any repercussions may be upon you as well as the operating crews.
Of course if would be great not to have these in place, but that's the way it is.