The ITSO Specification is the UK technical standard for interoperable smart ticketing.
The Specification defines the key technical items and interfaces that are required to deliver interoperability between the components of a smart ticketing system – smart media, point-of-service terminals and back offices – and between separate ticketing systems.
Its purpose is to provide a platform and a tool-box for the implementation of interoperable contactless smart customer media in public transport ticketing and related services.
ITSO Technical Specification 1000: Interoperable public transport ticketing using contactless smart customer media. Version V2.1.4.
ITSO TS 1000-8 is only made available to organisations which have signed a Non-Disclosure Agreement (NDA) with ITSO. See here.
For all other parts of the ITSO Specification see here.