MGW limits apply to the MGW of the truck, not the actual so he was in the wrong place.
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Maximum Gross Weight (MGW) is defined as what the vehicle can take when loaded, in this case as it had 6 axles, it would be capable of carrying 44 tonne, so for it to be legal for it to be there the sign would need to say 44 MGW
The rules apply whether the vehicle is empty or full, it's what it can take that makes the difference.
Lots of truck drivers get caught out with this.
But to answer your original question...
Unit will be about 10/11 tonne and trailer about 8/9 tonne giving approx 24/26 tonne payload.