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?
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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!