
First time something similar happened to us (our pup swallowed a rope) we went haring off to the vet's who gave her a small handful of washing soda to eat.
Very scientific we thought, but back came the rope and no harm done. Since then we have kept a supply of washing soda in the kitchen, have used it twice more with the same result. Friends with different vets have either had to have an injection which seems to make the dogs groggy as well as sick, (one Springer, two socks - different times :-( ) or in one case a big operation to remove a towel from their dog's gut - at a cost of £2000+. If you're worried, phone your surgery for advice.
Good luck.