A digital television receiver for use in a digital television broadcast system in which a plurality of digital television data streams can be provided in respective streams of television broadcast packets forming the lowest layer of a layered digital television structure and also in respective streams of Internet protocol packets forming the lowest layer of a layered Internet protocol structure, at least the streams of television broadcast packets being broadcast with a plurality of tables indicating where data of one layer of one structure can be found in another layer of one or other of the two structures, the received plurality of tables being used to determine where data contained in one layer can be found in an adjacent layer so as to construct tree structures or a new table allowing determination of in which stream of television broadcast packets the television data of a selected stream of Internet protocol packets is found. A two-stage process for identifying an alternative stream with television broadcast packets containing the same television programme is also proposed in which, first, identical transport streams are looked for and, second, the stream of Internet protocol packets containing the television programme are used to identify alternative streams of television broadcast packets containing the same television programme.