When should you check the tyre pressure?

You answered correctly. Tyre pressure should be checked regularly when the tyres are cool, because driving heats up the air inside the tyres and can give you an inaccurate reading. It is also important to check tyre pressure directly after a tyre change to ensure that the new tyres are properly inflated. Checking after every journey is not necessary and is not standard practice—regular checks and after fitting new tyres are sufficient for safety and proper vehicle performance. Always check when tyres are cold and after any tyre change for the most accurate results.