You can take part in Question Time even if you haven’t got a question on the Order Paper. Once an MP with a question on the Order Paper has asked their original and supplementary questions and the minister has replied, the Speaker may call other MPs to ask a supplementary question too. Stand in your place to indicate that you would like to ask a question. The question must be on the same subject. The Speaker will try to call MPs from alternate sides of the House.
If you have a question on the Order Paper, you can still ask a supplementary to someone else’s question, but you will then lose your chance to ask your question on the Order Paper.