Best case scenario
England goes into a recession which the BOE fights with QE infinity and rate cuts and that last about 8 - 12 years while trade deals are being discussed. The United Kingdom and EU stay together despite it all with Britain having a lesser voice in global affairs.
Worse case scenario
The EU unravels resulting in a economic catastrophe especially for the smaller countries, Britain is blamed for it all and the whole block goes into recession with some countries going into depression with Russia greatly benefiting from the chaos.