Yes, in the short term indeed. However, this is normal as markets don't like uncertainty , but as they get used to the new normal they will stabilize and growth will resume.
Being out of the E.U doesnt means we are out of Europe, just like not using the Euro doesnt means we are out of Europe. There are several European countries who dont use the Euro and who are not part of the E.U yet that doesn't make them not European.
At thw end of the day, markets are like human beings, once they get used to something its business as usual.
So any fall in our markets is temporal, short term and expected. no big deal.