Britain's electoral commission launched an investigation on Friday after queues of voters were unable to cast their ballots in the general election before polls closed. People waiting to vote in Thursday's election were locked out of polling stations across the country when they closed their doors at 10:00 pm (0900 GMT), while some places ran out of ballot papers. 'It is a cause for serious concern that many people who wanted to vote today were unable to do so by 10:00 pm when polls closed,' said a statement from the commission. 'The Electoral Commission will be undertaking a thorough review of what has happened in those constituencies where people have been unable to vote,' it added. Lawmakers expressed shock at the turn of events, and Justice Secretary Jack Straw suggested there could be legal challenges to close results in some areas where voters could not cast their ballots. 'For sure you could anticipate if there were significant numbers of people who were turned away and the result was very narrow... I'm sure they could seek legal advice,' Straw told Sky News television. There were reports of people being unable to vote in London, and the cities of Sheffield, Manchester, Liverpool and Newcastle. In London, police said they called to a polling station in the Lewisham district where around 300 people were yet to vote before it closed its doors. In the Hackney area, at least 150 people were still queuing when the polls closed, according to Andrew Boff, a mayoral candidate for the Conservative party. In the northern city of Sheffield, a number of voters -- mainly students -- were turned away after attempting to vote shortly before the deadline. 'We got this wrong and I would like to apologise,' said John Mothersole, the official in Sheffield who oversees the voting. In Liverpool, northwest England, some polling stations ran out of ballot papers because of an unexpectedly high turnout, according to local authorities. At least one polling station was shut for an hour and some voters did not return to vote after being turned away, said local lawmakers. The official overseeing the vote in the area apologised but insisted everyone who wanted to vote 'had the opportunity to do so.' 