That does explain alot.
Meanwhile, our friends at Hammer have announced the UK BD/DVD release of The Mummy for October, and in doing so say this:
...THE MUMMY has been unavailable on any Region 2 home entertainment format since 2004. The previously available DVD was authored at the incorrect aspect ratio of 1.77:1 and widely criticised by fans. The Region 1 edition, still available as an import, is also presented incorrectly at 1.77:1. This new release on Blu-ray and DVD double play presents the film in its original UK theatrical aspect ratio of 1.66:1 for the first time, as well as featuring a host of brand new extras never seen before and in high definition.
Containing 2xDVD + 1xBlu-ray. Features include: Original UK theatrical aspect ratio: 1.66:1 (the film has never before been released at this aspect ratio);
Alternate “full frame” aspect ratio: 1.37:1