It seems to me that with a rosy future outside the collapsing EU, the pound should be going up. They say it is because the world believes that we will get a bad deal from our negotiations with the EU, but with the UK as a net importer of EU goods ( especially from Germany ), shouldn't the EU be coming to the UK to try to negotiate terms with us?
Effectively everyone is now worried because Theresa May or whoever it is in the current UK PM spot said that they have a general date for when they want to officially leave the EU and trigger Article 50, which they pegged at somewhere March 2017. This means that there is basically no hope of them staying in the EU now, and even though there was little before it has a more profound effect now that there is no chance.
As for the negotiations, Germany is probably going to spite the UK during trade deals and try and give them the worst ones possible, and a big issue is that the UK doesn't export to a ton of places in general. If there were more trade partners with the UK, chances are the market would be less nervous.