Read the final report here

The aircraft was departing from Runway 26 at London Luton Airport, but when the PF made a normal aft movement of the side stick control at rotation airspeed, the aircraft did not pitch up. The PF increased the side stick input close to the maximum deflection. When the aircraft still did not pitch up, the PM selected TOGA thrust. The aircraft responded and a climb was commenced but then the pilots forgot to retract the landing gear till about 5000ft.