Mostyn No.1 is one of two new signal boxes built in 1902 in connection with the quadrupling of the north Wales main line. No.2 box, at the western end of the station, has since been demolished but No.1 box is still in use. It is a London & North Western Railway type 4 design, but with three storeys: the two lower floors are in brown brick and the operating floor is timber-framed with horizontal weatherboarding, under a pitched slate roof with decorative gable finials. On the northeast side the operating floor is cantilevered on brackets and the entrance is on the southeast gable end, reached by an open timber staircase. The box retains its original frame from 1902 with 40 levers.
Sources include: Peter Kay, Signalling Atlas and Signal Box Directory (Third Edition), Signalling Record Society, Wallasey, 2010; Network Rail, Signal Box Register (undated). For further information on the types and designs of signal boxes see: The Signalling Study Group, The Signal Box - A Pictorial History and Guide to Designs, OPC, 1986.
B.A.Malaws, RCAHMW, 31 March 2015.