Yes you can if you book the crossings yourself. The Caravan Club and other tour operators usually ask you to book your outward and return crossings with one company - not necessarily on the same route. A one way crossing with DFDS at the moment is from £45.00 upwards, the tunnel is likely to cost a lot more than that and I don't think you can use Tesco vouchers for a one way Eurotunnel crossing.