Just wondered as I (and a few more) got stuck on a country road early this morning behind a wide load and he was taking up about half of the oncoming lane as well as his own side. There were several dodgy moments on blind bends with oncoming traffic!
If you want to wait while I look back in my PCP file, I'll get the exact size, but I seem to remember something about 3 metres requiring police notification, 3.5 and extra person "assisting", I think it's about 4+metres and over for an escort. BICBW.