The relaunch is the last piece in Guardian Newspapers' 100m switch to the 470x315mm format, which has included installing two MAN Roland Colorman presses at a new plant run by Newsfax in East London and at Trafford Park Printers in Manchester.

A spokeswoman for GNL said that the initial print run would be "on the generous side" in expectation of a healthy jump in sales, although she declined to reveal a figure. Circulation for The Observer stood at 408,452 for November, down 5.4% year-on-year.

The Observer has also undergone a major redesign, with a stitched half-Berliner TV section and a new monthly magazine, Observer Woman.

The move signals a major contract loss for Docklands printer West Ferry, which is owned by The Telegraph Group and Express Newspapers.

Legal proceedings between GNL and West Ferry have taken place over the move, in which GNL broke a contract that was meant to continue until 2009. No details of the proceedings have been disclosed.