Actually, I often find that a good cream will start to ripen and turn towards creme fraiche after a while. So I'll often keep things like that well past the sell date. As long as it doesn't go mouldy, give it a taste!

We don't get double cream here in the States - our loss - but if it behaves similarly to creme fraiche or heavy cream, yes you can freeze it, tightly wrapped. It may separate/weep when it thaws, so you'll want to use it in cooked or baked applications and not as a topping for a dessert.

Also, I'm not how conservative your "use by" system is, but in my experience, if I've kept a soured or creamy dairy product unopened and very cold I've been able to use it at least one week past the use by date.