The man who masterminded an overhaul of the way the Commons works has defended the move.

As MPs begin returning to Westminster, leader of the Commons Robin Cook has said that starting parliamentary debates earlier will help raise the profile of British politics.

Cook said changes such as moving prime minister's question time to midday on Wednesday would also ensure "more clear coverage" of political issues by the media.

"A lot of these changes are not just about the change in the hours, important though that is. It's about making parliament more effective, more topical," he told Sky News.

The first full day of the new arrangements will come on Wednesday.

Cook said that the new way MPs do business would "set the agenda for the day rather than parliament simply to be seen to be responding to the agenda set by others".

"None of us have a press conference at 4.00pm in the professional world and that's when major announcements of government policy come on in the House of Commons."

Cook promised the changes would help in bringing ministers to account.

"I genuinely believe that what we are doing will provide for more effective parliament and will keep government on its toes," he said.

Downing Street admitted it had been caught out by the switch in hours - new times for its media briefings have still to be decided.

In a series of votes last October, MPs backed plans to start the chamber's eight-hour day at 11.30am on Wednesdays and finish earlier on Thursdays by a majority of 77.

Proposals for the Commons to start at the same time on Tuesdays were approved by a majority of just seven.