As a london messenger of 3 1/2 years and not one single accident, do NOT piss about with hgvs, if its ahead, let it go, whats it gonna save you time wise eh? Give them as much space as they need and stay where you can be seen. Having spoken to the police on this matter more than once, even experienced riders have thought ahh that’ll be ok…..nah afraid not sunshine….don’t even think about it, stay out of their way and stay in one piece….oh and obtain the 6th sense, knowing what a vehicle will do before it does it…they all have body language, know how to read it, it saves me shit everyday or so.
Never ever undertake an HGV, it’s simply not worth the few seconds you think you’ll gain.