Make a cloud in bottle
Map of UK, 2 litre bottle, bag of ice cubes, matches, warm water
Discuss with scouts how air masses affect the UK and how weather fronts and clouds are formed with warm and cold air. Scouts then put about 1 inch warm water in bottle (move around sides to clear steam if necessary) let match burn and then blow out and drop in the bottle to represent dirt particles in atmosphere. Do up lid and lay bag of ice cubs over the top of the bottle. A cloud will gradually form below the ice. A sheet of dark paper can be held behind to make it easier to see the cloud.