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.
Biscuits are notorious for that; they're best eaten right away. If you want to preserve their original texture longer than 12 hours (yes, that short of a time), your best bet is to freeze them as soon as they are cool and eat them within a month or two. Wrap them as air-tightly as possible.
You can pop the frozen biscuits in a moderate oven or unwrap and give them an hour or so on the counter to defrost, then warm them. Either way, it's best to serve them warm, they will seem softer and fresher that way.
If you've found a recipe you like and think you might want to make them frequently, mix the dry ingredients for multiple batches. If you can weigh the dry mix that you have just mixed, then you're golden. You can make as many or as few biscuits as you want anytime just by using the same proportion of dry, fat and liquid as the original recipe. You can easily make a single biscuit that way or feed a crowd.
Best Answer
Just put them in the oven at 100 °C (212 °F, the boiling point of water) and all the humidity will dry out naturally.
The time depends on the size and amount of water in the biscuits: