Celebrate at the finish line
Finish lines bring out many different emotions in people. The moment is special but fleeting. You are all working so hard towards your moment. If it is your first, I want you to think about it in the run up and celebrate it hard when it comes because it will be over before you know it. They are special and the thing is you've earned the right to act however you want when you cross that line as long as it doesn't involve punching people. Be proud of your achievements to date to get you to where you are and those that are to come. Your finish line would be a good time to be non typically British where you just wander off without letting it all out. Think about it in the run up to your event. Celebrate it on the day.