Wall Street's biggest investment banks will not waste time in reviewing their European businesses as capital markets issuance and M&A activity slow after the UK’s vote to leave the EU, according to analysts at credit rating agency Fitch.

Fitch, which on June 27 downgraded the UK's sovereign credit rating from AA+ to AA, said in a statement that the June 23 referendum vote to leave the EU would be "disruptive" and "costly" for US banks with big UK businesses.