If rumours alone for Brexit is disasterous for the pound, it's scary to think what would happen should Brexit actually occur, eh!
The shitkicking the UK economy is taking isn't because of rumours, and it's not a prelude to actual Brexit. It's the uncertainty. If the UK had actually left the EU promptly, rather than infighting, back-biting, plotting, machinating, complaining, denouncing, resigning, grandstanding, begging and impeding then it would be done by now.
Who wants to invest in a country that may or may not be subject to EU rules in a month? Or three? What if they sob and beg and turn on the waterworks for yet another extension? Investors hate uncertainty.