The ''use by' date was imminent so I put the unopened double cream tub in the freezer as I can't bear waste - does any one know how it will turn out once defrosted and can it be used as 'normal' or what can it be used for?
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.
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!