1. An apparatus for decoding a recursive convolutional encoded bitstream, comprising: a decoder adapted to decode a non-recursive convolutional encoded bitstream; and a post-processing element arranged to receive the output of the decoder and apply a post-processing operation thereto; the decoder and the post-processing element operable together in turn to decode a received recursive convolutional encoded bitstream to provide a decoded bitstream; wherein the post-processing element includes a non-recursive (NR) encoder having a generator polynomial matrix G NR of generator polynomials g: G NR ⁡ ( D ) = [ g 1 , 0 0 … 0 0 0 g 2 , 0 0 0 0 ⋮ 0 ⋱ 0 ⋮ 0 0 0 g k - 1 , 0 0 0 0 … 0 g k , 0 ] , where k is an integer greater than or equal to 1 and D is a bit delay.