RS 307-468, which is a house coded part supplied by RS. Not available in the online catalogue, but probably is in the paper catalogue as a discontinued part number. If a single opamp it will be a 741or a 308 most likely, or if a dual any one of many generic audio amplifier chips. Single you will have to see where the offset pins are connected to determine if 741, offset to -15V, or 308 offset to +15V.