To drive defensively in a UK driving test, you should:

1. Keep a safe distance from the vehicle in front of you, as this will give you more time to react to any sudden stops or turns.
2. Look well ahead of you when driving, and be aware of any potential hazards or changes in the road ahead.
3. Anticipate the actions of other road users, such as pedestrians, cyclists and other drivers, and be prepared to take appropriate action to avoid collisions.
4. Use your signals when changing lanes or turning, to let other road users know your intentions.
5. Follow the speed limit and obey all traffic signs and signals.
6. Avoid distractions while driving, such as using your mobile phone or eating.
7. Always wear your seatbelt and ensure that any passengers in your vehicle do the same.
8. Always be prepared to stop or take evasive action if necessary.
9. Be aware of vulnerable road users such as pedestrians, cyclist, and motorbike rider.
10. Always be ready to take the right of way if it is safe to do so.

Remember, defensive driving is all about being aware of your surroundings and anticipating potential hazards, so that you can avoid accidents and stay safe on the road.