In addition to covering costs, travel insurance also makes things easy in case something happens. For example, your insurance company can provide you with a list of clinics they have agreements with, that can bill the insurance company directly. This way you don't have to use your credit card limit, or pay in cash.
And the clinic will treat you well, knowing they can charge the insurance company. So, it's additional quality aswell.
I suppose 6 pounds is a bit suspect, I have to say. I'd read the fine print carefully.