Nearly two-thirds of British businesses are "optimistic" about their future in the wake of the Brexit vote, a major survey has disclosed.

A poll of 34,000 companies by the Institute of Directors found that 60 per cent of businesses are "optimistic" or "very optimistic" about the year ahead.

The businesses, predominantly small or medium-sized, conceded there is "uncertainty" of the vote to leave the European Union.

However, their positivity is in marked contrast to comments by the bosses of Britain's biggest companies, some of whom have criticised Brexit and even threatened to relocate out of the U.K.