Interrail or Eurail are not valid on London Underground services. National Rail stations: Paper Passes and mPass Barcodes cannot be used to open the gates on the National Rail network of Great Britain directly, however, Passes are accepted at the side gate* of any gated station on the network.

No, you cannot use a Eurail Pass (or an Interrail Pass) on the London Underground (the "Tube"), nor can it be used on London's red buses or the Docklands Light Railway (DLR). These services are operated by Transport for London (TfL), which is a separate entity from the National Rail network. To navigate London's local transport, you must use a contactless payment method (such as a credit card or mobile phone) or an Oyster Card. However, the Eurail Pass is fully valid on "National Rail" services that operate within London, such as the trains that run from Waterloo to Clapham Junction or from Euston to Watford. If you are arriving in London via the Eurostar from Paris or Brussels, your Eurail Pass covers the long-haul journey into St. Pancras International, but once you step outside that station to enter the Tube station below, you will need a different ticket. While it may seem inconvenient, this distinction is standard across most major European cities where the local subway and the national trains are run by different authorities.