I have public liability, but I am never sure whether it is a legal requirement if you are self employed.
I do know that employers liability is a legal requirement and I am sure I have read on the boards that puplic liability isn't.
I know that you most certainly need to have it if you want commercial jobs as many companies want to see a copy of your policy. I have no doubt that more and more domestic accounts will also want the assurance that you have public liability.
But you won't need to carry your actual certificate, just keep a handful of copies in your glove compartment
Ian