This could be a great resource for genealogists researching employees of Thomas Cook Travel. It also contains some passenger lists but certainly not all of them. Quoting from an article by Paul Grinnell in the Peterborough Telegraph web site:
The archives that were for years stored in the Thomas Cook offices in Bretton and more recently at Lynch Wood have been sold to the Record Office for Leicestershire, Leicester and Rutland.
The record office, which is run by Leicestershire County Council with Leicester City Council and Rutland County Council, secured the right to house the internationally significant collection following a bidding process following the holiday giant’s collapse last year with the loss of at least 1,000 jobs in Peterborough.
The entire Thomas Cook archive, which encompasses records from the earliest days of package travel right up to the modern day, is now being transferred to the record office in Wigston, Leicester.