Thanks safeware,
The HSE doc is interesting reading, and has a refreshing tone on how common sense needs to be applied to assessing risk.
I'm a bit rusty here, but I was under the impression that projects had to set specific targets, which was based on HSE / comparative projects but can take other factors into account (the "gas leak" example in the HSE doc is interesting in this respect). Hence in theory the Nimrod (or any other a/c) safety targets could still be different/vary from other comparative aircraft. Is there a copy of JSP553 on the interweb, or can you paraphrase the bits relating to safety targets?
Re my question on oil-rigs etc. if I understand the principle correctly the HSE outlines / can advise on a certain rate of risk to people that is publically acceptable, and uses this to set targets for/regulate operators (i.e. an oil rig operator would need to show how his procedures and systems supported meeting/exceeding the acceptable risk to people rate). Interesting to read that you're more at risk farming than working on oil rigs.