Can tomato paste be substituted for tomato purée?
I'll weigh in on this one, having extensive cooking experience on both sides of the pond. The terminology is indeed confusing when it comes to tomato products. By tomato sauce they don't mean canned tomato sauce like you get in the states, they actually mean ketchup! As for puree there's two types, one is just what it means, pureed tomatoes in a can, and the other is super-concentrated like what in the US is called tomato paste and comes in a tube. 

Given it's this recipe is asking for 250ml of puree they must mean the canned stuff, as adding that much concentrate would be hideous. To replicate UK/AU style tomato puree I'd use a can of tomato sauce with a half mini-can of tomato paste to thicken it up a bit. That still sounds like a bit too much liquid for my taste. 

Alternatively you can use my mom's technique and add a can of concentrated tomato soup to the mix, it makes a great meat-loaf!