The polls are open across the United Kingdom in the tightest General Election for generations.

Voters are deciding whether Prime Minister David Cameron will return to 10 Downing Street - or whether to opt for Labour's Ed Miliband.

The make-up of the next Parliament should become clear by tomorrow morning - however several weeks of negotiations are expected before either of the big two parties can form a government.

The polls show the race is still too close to call - and Dr Ben Lauderdale of London School of Economics says Scottish nationalists could tip the balance of power: