IWM will let you take copies of anything for private research/use but permission is needed if you intend to publish through print, public lecture/talks or online etc. Official documents or other published material - books, pamphlets etc can be quoted from under the "fair dealings" bit of copyright law but not private papers. If you need to quote extensively from printed stuff or use private papers in any proposed work you intend to publish or put online you need copyright owner's permission. For private papers IWM will facilitate this for you and also provide sample request letters for you to use. I have found IWM to be very useful - yes you do have to book to visit and request material 5 working days ahead but their online catalogue knocks TNA into a cocked hat so it is very easy to identify what you want. The private papers are pure gold that adds so much to the war diaries and other official material from TNA. (And for those of us north of London and train dependent, Lambeth is soooo much easier to get to than Kew).