Over hanging loads

Its 2m maximum, over 1m it must be marked.

3m at the front.

Up to 2.9m width, not marked.
2.9m to 3.5m, must be marked.

Over 3.5m must be escorted.

I hope I am right with these.

Can someone clarify, I have been told if using an extendable trailer you can go up to 18m with no markings? Over 18m must be rear steer too?

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