Because of Brexit the rest of the world has lost confidence in the British economy and currency. It is not yet clear how Brexit will work and so it is understandable that people are reluctant to put their trust in the British economy, as it is possible that Brexit will be catastrophic for British businesses.
Without the European economy to back it up, people no long have faith in the economy of Great Britian. The pound will continue to fall. Theresa May's comments about Brexit did not help. Great Britain is doomed, and it is no longer the great country and major power it once was.
I understand people want to go back to the good old days, but that ship has sailed. Due to technology we are more connected than ever before. Increased international way is the way forward for business and the markets are just showing their frustration with Britain for turning its back against the world.
The pound has performed better than the Euro for many years. There are highs and lows in any currency. The pound is falling right now because the dollar is so strong. The dollar is strong all around the world, not just against the pound. The pound will recover when the dollar falls off.