Not necessarily that, I think it was more to do with the belief that big business would be spooked and confidence plummet...hence the pound would do the same. Pure speculation
But that's exactly what currency dealing is. They mark currencies up or down depending on events. Yesterday MaccyD promised to renationalise almost everything and cancel all PFI deals. No mention of how this would be paid for (except that they would raise taxes and force everyone to pay them - I don't understand how nobody thought of this before). So perhaps there is a shred of reality in a threat on the pound.