British PM David Cameron has just voted in the EU referendum at a polling station around the corner from Downing Street. He was accompanied by his wife Samantha.

Voting started on Thursday in a historic referendum on whether the United Kingdom should remain within the 28-nation European Union or leave with opinion polls showing a very tight race that could go either way.

An estimated 46,499,537 people are entitled to take part in the vote -- a record number for a UK poll. Polling stations opened at 11.30 am IST and will close at 02.30 am IST on Thursday.

Opinion polls have suggested that while big business is broadly in favour of staying in the EU, small firms have been evenly split in what looks like a photo-finish with one poll showing Remain at 45 per cent and Leave 44 per cent, with 11 per cent undecided.

British Prime Minister David Cameron on Wednesday made a last-minute plea to British voters not to give up the best of both worlds by voting to remain in the EU.

Leading Brexit backer Boris Johnson, a former London mayor who is widely touted as a future prime minister, insisted the Leave campaign was on the brink of victory.

Image: UK PM David Cameron and his wife Samantha leave a polling booth in London. Pic: Reuters