no according to megatrain terms and conditions as below...
6.Journeys are only available for travel in Standard Class. A Weekend First Upgrade is available on East Midlands Trains at weekends and public holidays, subject to availability.
7.Megatrain booking references cannot be used in conjunction with any National Rail, East Midlands Trains, Virgin Trains or South West Trains promotion or offer unless stated otherwise. (This includes, but is not limited to, PlusBus and discounted admission tickets to attractions.)
8.Seat reservations are not available on megatrain services.