A common interface controller and a method of descrambling channels of first and second transport streams using a conditional access module for descrambling channels of a transport stream as identified by respective PIDs wherein an intermediate data stream is provided by time multiplexing at least a part of the first transport stream with at least a part of the second transport stream, the part of the first transport stream including a first channel and the part of the second transport stream including a second channel, and wherein the original value of a PID identifying the second channel is changed to an intermediate value not used by any PID of any respective channel in said at least a part of the first transport stream such that the intermediate data stream forms an intermediate transport stream for processing by the conditional access module.