I have been driving HGV 's for nearly
20 years but have recently gone the LTD driver route.
I have spoken to various people as you do with regards to insurance I might need. From what I have heard public liability insurance is only optional and not a legal requirement and as a freelance driver I am all ready covered under any companies motor insurance policy when driving there vehicles.
When I’ve worked as a sole trader doing van work in my vehicle I have had PL insurance.
If you were going to be exposed I suppose it would be a scenario where say a building is damaged though fault of your actions and the company decline liability as the cause was down to you (make an example - runaway vehicle due to no handbrake not mechanical failure).
PL Insurance has always been pretty cheap compared to other cover I have generally had cover to £5 million for around £120 (but as van courier).