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.
UPDATE: recently I started using drier starter with bread-dough like consistency and add it when it's about room temperature. Measuring the ingredients precisely also helps, provided you figured out the proper ratio of flour and water.
My solution: simply use more starter. Generally the starter is kept in the fridge in a jar. I take out the jar from the fridge, add around 150g of flour and 150ml water. After an hour or two, once there are bubbles on the surface, I just add around 300g of this mixture to the bread. The jar (with little starter left) goes back to the fridge. The
Best Answer
Oven spring is caused by the air pockets in the dough expanding from the heat. (Dough rises from gasses released from the yeast.)
After the shaping and final rise, often times there is a light, dry "skin" over the dough. By slashing a dough before it goes into the oven, you break this skin, and the bread is able to expand. If the loaf is a "fancy loaf" and you can't slash it without ruining the appearance (like a braided loaf), try to keep the loaf from drying out with a light mist of cooking spray after shaping and before the final rise.
Perhaps the bread is cooking too quickly when it hits the heat of the oven, essentially cooking a crust before the air pockets get heated enough to expand? Baking in a moist environment should help with that. Place an empty, sturdy pan (I use a cast iron skillet) on the bottom rack of the oven (or directly on the floor of the oven) before preheating. When you place the bread in the oven, pour about 1 cup of very hot water into the empty pan. This will create a bunch of steam, and help prevent the bread from crusting before it gets its "spring."
If you have a pizza/baking stone, use it. Having a hot surface to set your pans on helps with the rise. Think about it... you open the oven door, and out goes a lot of the heat... even though the walls of the oven are retaining the heat, it will take a little while before that heat reaches the bread. Setting the pan on the stone will give you that instant heat on the bottom, causing dough to rise from the bottom up, rather than just getting a small rise from the top area.
If you don't have a stone, invert a heavy baking sheet, cast iron griddle, or something similar, and heat that up in the oven the same as you would for a baking stone. Invert the sheet pan so it's easier to slide your bread pans on and off the hot pan without having to deal with a small edge.
If you haven't got equipment to do the other options listed above, you can try the "cold oven method." Just put the loaf into a cold oven, and set the temperature. Don't preheat. The gradual heat from the bottom of the oven as it preheats will give you some of that "oven spring."
I use a baking stone and steam, but I have had great success with using an inverted aluminum sheet pan with steam before I got the stone... and before I learned that trick, I used the simple cold oven method (no steam as the oven is cold!).