Transaction identifier expansion circuitry is provided, along with a method of operating such circuitry. The transaction identifier expansion circuitry interfaces between a master device and interconnect circuitry used to couple the master device with a plurality of slave devices to enable transactions to be performed. Transaction analysis circuitry is responsive to each transaction in a sequence of transactions initiated by the master device, to compare at least one attribute of the transaction with predetermined attributes indicative of the target slave device for that transaction. Based on the comparison, an initial transaction identifier is then mapped to one of a plurality of revised transaction identifiers, such that the revised transaction identifier is dependent on the target slave device. Reordering circuitry is then arranged to buffer response transfers received from the interconnect circuitry destined for the master device, with each response transfer having the revised transaction identifier associated therewith. The reordering circuitry then re-orders the response transfers having regard to the original transaction order of those transactions within the sequence of transactions that had the same initial transaction identifier, prior to provision of each response transfer to the master device. By such an approach, the performance of a high performance master device can be maintained, by ensuring that for at least the transactions targeted to a particular subset of the slave devices, no intervention by deadlock avoidance circuitry within the interconnect is required when routing transactions to those slave devices, due to the use of different transaction identifiers when accessing those slave devices.