I hope that the "Unsolicited Goods and Services Act 1971" would come into play here. I haven't been able to find a copy online (don't really know where to look; Google isn't being that helpful) so don't know for sure. I will phone trading standards and see if they can fill me in.

To me the situation we face with ParcelForce is exactly the same as if you had a garden, and one day while you were out, a gardener came around and did it up, without you asking them to, and when you return, expecting you to pay for it. In that case I would not expect the gardener to be able to enforce payment, and similarly I find it difficult to believe that ParcelForce should be able to enforce payment for their unsolicited service.