Ian Robinson, co-owner of a small investment firm in London, is watching Britain's general election this Thursday with unease.

A victory for Prime Minister David Cameron's Conservative Party could bring Britain a step closer to leaving the 28-nation European Union, a move many companies fear would cause damage by increasing costs of doing business on the continent and eroding London's role as a global financial hub.

Robinson says leaving the EU would make even the most basic things more difficult for businesses in Britain, forcing him to apply for licenses in each country where he operates rather than getting a single permit from British regulators.