Click photos to see the full size version in the image database.
This foldout pamphlet is aimed at the U.K., French, and Benelux regions of Europe. In particular, I believe this is a French catalogue that was included in the TGV set. Although some parts of the Thomas series are shown, as the catalogue notes the Thomas range was only available in the UK (out of the mentioned territories) at the time. The apparently primarily French Super Set, based on the Thomas Big Set, is shown as well as the aforementioned TGV Set.

The range of trains and cars is shown, including new-for-1999 trains that were specifically European like the Virgin Train, Eurostar Train, and orange TGV. The accessories and rail are also shown, including four packs of the Straight Rail & Road and Curve Rail & Road sections from Motor Tomica that weren't available in the UK...
The inside of the catalogue is a foldout poster that shows more of the promotional layout from the cover with accessories and vehicles called out.