A decoder comprising a decoding element arranged to operate in a first mode for decoding a turbo encoded data stream and in a second mode for decoding a viterbi encoded data stream, wherein the decoding element is responsive to a first control signal for switching from the first mode to the second mode during decoding of a turbo code block and responsive to a second control signal for switching from the second mode to the first mode to allow continued decoding of the turbo code block.