The UK weather is so changeable that it is often the topic of conversation between people who live there. It never quite does what you expect! In winter time it can get pretty cold with temperatures below freezing at times and some snow. The more north you go, the more snow and cold weather you get with guaranteed snow in winter in Scotland, but a very low chance of any snow on the south coast. In the summer it can get muggy at times and temperatures can go over 30 degrees but it is rare to get that hot. It is breezier and cooler on the coast. Usually there is a lot of rain at any time of the year.
This means that whenever you visit you will need to be prepared for all sorts of weather. It is always wise to be prepared for wet weather. This means that you need to carry waterproof clothing as well as good footwear and possibly a rain hat or umbrella all of the time. You also need to consider where you will put the items to dry when you return to your accommodation or when it stops raining and you want to remove them.
All year round it is possible to get your skin damaged by the sun in the UK. This means that you need to be prepared to use sun protection whenever the sun is shining and it is hot. This means using a high factor sun cream and/or covering up so that you do not get burned. Although the UK is not known for its hot weather, there are hot days and it is possible to get burned easily. At times it can be cool for a few days and then very hot and this can catch you out and means that it can be easy for you to get burned as you are not prepared. Windy weather can also mean that it feels cooler than it actually is and if it is a warm day can mean that you are more prone to getting burned by the sun. In the cold weather it means that you will need to put on extra layers if it is windy as it will feel very much colder.
The changeable nature of the weather means that it is sensible to pack lots of thin layers so that you can keep yourself warm if necessary but remove layers of clothing and cool down if you get overheated.