Note that this is not the same deal as previously posted as also now inc destinations apart from London. Hope it helps someone.
megabus has released a number of FREE seats for travel between popular UK cities in February and March.
Weve scoured the site and can genuinely report that the following fares are available for just 50p, return (which covers the online booking fee).
London to/from Cardiff
London to/from Sheffield
London to/from Birmingham
Manchester to/from Birmingham
Manchester to/from Newcastle
Manchester to/from Oxford
Birmingham to/from Leeds
Leeds to/from Southampton
Availability is limited to midweek travel (Monday-Thursday) in February and March.