In NZ normal pure cream is close enough to "double cream" in performance, it's around 35% to 40% fat. By general global definition it should be called "heavy cream"
NZ cream is pure skimmed cream from fresh milk, and does not need thickening or other processing to produce excellent results as a whipped product, or for a thick cream additive in sauces or fillings
Cream can get a little seasonal just after calving time (Aug), but in general it's just perfect
The export variety is often labelled "Culinary Cream" and is 38% fat or higher. This is what many people around the world would consider NZ cream (other than NZ butter or AMF)
If you want closer to 50% fat cream, ask your local farmers for some raw milk and skim out the lumps of fat from that. Let the milk settle overnight and skim the cream from that. Then gently heat the fat lumps to melt and carefully mix into the skimmed cream. Not for the faint of heart!
NZ "Thickened cream" or "Mascarpone cream" is standard pure cream with a thickener like E1442 added, you can make your own too
You need to make sure you use the right measurements when translating recipes from the US to the UK as the UK uses imperial measurements which are different from US measurements. There are also differences in cream fat content and egg sizes. Teaspoons and tablespoons are the same, so don't worry about them.
First, pint measurements, as the UK doesn't use cup measurements. The UK pint is 20% bigger than the US pint, so if you are using UK pints to measure you may be getting ratios wrong. Use Milliliters instead when translating. 1 US Cup is 237ml (I round up to 240). If you use UK pints as a measure instead of US you won't have enough baking powder in the ratio. In fact, I find UK baking powder and bicarb a bit weaker than US powders, so I increase those measurements a bit anyway.
What works for me is the first time I make a US recipe in the UK I weigh the dry ingredients and use weights every time I make the recipe after that, I can fine-tune it that way.
US light cream is between 10-30% butter fat, and heavy cream is about 36-40%. UK single cream is between 10-30% fat, whipping cream is about 36%, and double cream is 50% fat. So if you are right that US heavy cream is UK whipping cream, but mixing 2 parts UK double and 1 part single works just as well as many places don't stock whipping cream.
I doubt that your results come from the cream you are using though, the fat contents aren't that different. One thing that could be different is the flour you use. US and UK flours aren't completely the same. For my biscuits in the UK I buy 00 or purpose milled pastry flour, which is finer and better for pastry than the bog standard stuff. If you can't find it pick the flour with the lowest protein content you can find.
Hope this helps, let the forum know your results if you can.
Best Answer
Heavy cream and heavy whipping cream are almost the same thing. The only difference is the amount of fat they contain. Heavy cream contains about 36% fat, while whipping cream contains only about 30%. (That means that heavy cream actually produces better, thicker whipped cream!)
Since this is going into a cheesecake, I think that this will be an acceptable substitution. The amount of cream included in cheesecake recipes is usually quite small, and used primarily for thinning the mixture. Cheesecake is already high in fat, so the addition of a little more is unlikely to matter, especially in such a small quantity. I would not expect any difference in flavor or texture in the finished cake.