I just did my shopping at Sainsbury's and they had buy-one-get-one-free on the entire Linda McCartney range. They've done this before with the odd item, but never the entire range. In my experience they usually sell out quickly as well (or they're just poor at restocking the shelves) so try to get there early in the day.
Off the top of my head, the products were:
Chicken style burgers
Vegetarian roast with sage & onion stuffing
Deep filled country pie
I decided to get one of each as I've always been very impressed with the Linda McCartney stuff. The lasagne in particular is nicer than any meat version I've ever bought.
It's available online as well but they don't have as big a range on there as they did at my local store.