There's a whole bunch of stuff (including 'Working at heights') available from the HSE web site - http://www.hse.gov.uk/pubns/conindex.htm

I don't have time to read it all I'm afraid - work beckons...

I think your 6m rule is likely to be "old-hat". I was speaking to a builder friend of mine yesterday about health and safety in relation to scaffolding. He said that there is a legal "duty of care" requirement on any structure (temporary or permanent) that can be used by people. This means that whoever erects the stucture can be held liable in law for any injury that somebody using the structure might sustain. He suggested that we talk at a very early stage of the plan to the health and safety inspectorate, let them know that it is a critical part of the project that we maintain historical accuracy as much as possible and ask them for advice on the matter. He said this is much better than going with a finalised plan of our own and having to argue with them.