From the no450 campaign website (http://www.no450.co.uk/)

"The no450 campaign was set up as a direct result of South West Trains decision to withdraw a considerable number of Mainline Class 444 Trains from the London Waterloo to Portsmouth City Stations , and replacing them with Outer-Suburban Class 450 Trains."

"These Class 450 Trains , with their 3+2 seating are cramped and uncomfortable , and are referred to as Outer Suburban Trains. When they were first procured , they were painted blue and fitted with suburban route maps , as opposed to the Class 444 Trains with 2+2 seating which are painted white and fitted with Long Distance Route Maps."

"The decision to re-shuffle stock appears to be a direct result of the South West Trains decision to withdraw the 24 Class 442 (White) Trains from the Southampton , Bournemouth and Weymouth routes and re-assign a large number of the Portsmouth Class 444 Trains to that route. There are 45 Class 444 Trains (5-car units) in the South West Train fleet."

"Many Class 450 Trains that now serve the Portsmouth route were re-assigned from routes such as Reading , where the Class 458 Trains, which had been withdrawn, were brought back into service."

Here is an interesting link from the no450 forum.
http://www.no450forum.org.uk/phpBB2/viewtopic.php?t=100&start=0&postdays=0&postorder=asc&highlight=

Quotes from the DfT :

"The new Gatwick Express service will begin in December 2008 under the same branding and with the same frequency to and from the airport. Luggage storage will continue be provided to accommodate the needs of airport passengers."

"Six Gatwick Express trains in the 90-minute height of the morning peak will start at Brighton, calling at Haywards Heath, Gatwick and London Victoria. Some will also call at intermediate stations including Preston Park, Hassocks, Burgess Hill and Wivelsfield. The same service will return southbound in the evening high peak. These trains will comprise a minimum of 10 carriages - compared with the current 7-car Gatwick Express trains."

"Extra carriages for the service are due to be provided by the leasing of several class 442 vehicles which are not currently in use."