The old BS5973 Table 19 indicated that a scaffold standing over 2 years should have an increased wind factor considered within its design.
Planning permission for Temporary structures may also be required by some local authorities and your client should deal with this directly.
Although many local authorities deal with this grey area in differing ways, some say if its on hire to the client and he is paying a weekly charge, then planning would not be needed,
but if you have a sign on it, then planning would be needed!
Best bet, leave it to the client to sort!