There is no such thing as a "set of plans" for a staircase! There are companies who sell kits, but that's not the same. Every staircase is individually laid out and set-out to fit the individual stair well and the going is adjusted accordingly (and if you don't kno what that term is you are not yet competent to build a staircase). To find out what the Building Regs are why not get hold of a set of the Building Regs? (from HMSO).
Unless you are capable of working to a good degree of accuracy a staircase will be difficult - unless you understand the principles of ply/glulam lamination and/or torsion box construction as well a spiral staircase might well be impossible. Straight staircases are easy enough to do once you understand the principles, but many professionals shy away from making spirals.
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