Gents - thanks for your comments - I think I get the jist of it. I've done some homework and the answer is specific to scaffold as it is not a tower but actually a facade (a long tower). What we do is tie every other standard back to the building and then the ledgers (horizontals) stabilise...
Agreed - I would normally treat it as 1.5m also. However, my vertical column / truss is actually a scaffold subject to the scaffold code BS EN 12811 and guidance document from that TG20:08. In these they state if the structure is 6m high with 2m lifts, restrained top and bottom as my exmaple...
