According to the post on the airlineroute.net website, Planned last British Airways’ Boeing 737-400 operation for each route during the month of September 2015 as follow.
London Gatwick – Algiers Last 737-400 flight on 24SEP15
London Gatwick – Amsterdam Last 737-400 flight on 15SEP15
London Gatwick – Cagliari Last 737-400 flight on 14SEP15
London Gatwick – Catania Last 737-400 flight on 25SEP15
London Gatwick – Faro Last 737-400 flight on 26SEP15
London Gatwick – Glasgow Last 737-400 flight on 21SEP15
London Gatwick – Ibiza Last 737-400 flight on 01SEP15
London Gatwick – Jersey Last 737-400 flight on 21SEP15
London Gatwick – Malaga Last 737-400 flight on 23SEP15
London Gatwick – Malta Last 737-400 flight on 27SEP15
London Gatwick – Marrakech Last 737-400 flight on 24SEP15
London Gatwick – Naples Last 737-400 flight on 22SEP15
London Gatwick – Rome Last 737-400 flight on 16SEP15
London Gatwick – Seville Last 737-400 flight on 13SEP15
London Gatwick – Thessaloniki Last 737-400 flight on 27SEP15
London Gatwick – Tirana Last 737-400 flight on 11SEP15
London Gatwick – Turin Overall final 737-400 service on 30SEP15
London Gatwick – Verona Last 737-400 flight on 29SEP15
British Airways to End Boeing 737 Service in late-Sep 2015 | Airline Route