Sales of party manifestos are outstripping those for the last election - and outselling authors such as JK Rowling, figures have showed.

Book retailer Waterstone's said sales are up 160% on 2005, and there are still eight days to go before election day.

The biggest rise compared to five years ago is for the Lib Dems with curious voters driving a 250% boost.

But figures show the Conservatives are ahead with 38% of the total manifesto sales so far at Waterstone's, followed by the Liberal Democrats on 32% and Labour on 30%.

Sales of the Tory manifesto have spiked by 193% compared with 2005 levels. Labour is in third spot at 97% - which means they have so far failed to match sales for the last general election, although the election is more than a week away on May 6.

Collectively election pledges sold more copies than the books of the Harry Potter author at Waterstone's last week.

"This is clearly the most important election in a generation," said Andrew Lake, Waterstone's Politics Buyer. "I've worked in books for nearly 20 years and have never seen such demand for manifestos.

"These titles are outselling some of Waterstone's best-selling authors, including Nick Hornby and JK Rowling, and sales show no sign of abating."