The UK National Screening Committee helps keep people healthy by checking for any problems that might be hiding in their bodies. It's a group of people who look at all the different things that can go wrong with your body and decide which ones are the most important to check for.
Sometimes, even when you feel perfectly fine, you might have a problem that needs to be caught early before it gets worse. For example, when you're playing outside, you might get a cut that you don't notice. If you don't clean the cut and put medicine on it, it could get infected and hurt you. But if you check the cut and take care of it right away, you'll be much better off.
The UK National Screening Committee does the same thing for your whole body. They look at different problems that can happen (like cancer, heart disease, or diabetes), and figure out the best way to check for them. The tests might be things like getting a blood test, having an x-ray or scan, or even just answering some questions about how you feel.
Once they figure out the best test, they let doctors know so that people can get checked and treated early, before it becomes a bigger problem. They help keep everyone safe and healthy!