Have a look at www.tesco.com/clubcard and this will give you all the information you require. You have to exchange your Clubcard Vouchers for "deals". If you have the newer vouchers you are able to do this online.Once you receive your Clubcard Deal Vouchers ( which have a monetary value) from Tesco you can can then phone Eurotunnel and make your booking. You receive all the information you require from Tesco and Eurotunnel will repeat this when you phone to make a booking. I find the Clubcard Vouchers are great for bringing down the cost of ferry travel!