This seems to be the return flight of a one-off Vagar-Gatwick scheduled flight which was announced last month. The Vagar-Gatwick sector seems to have been flown on 27th May with the return planned for today. I don't know why it seems to have been re-routed to depart Southend instead.
Edit: Yes, I can confirm that seems to be the case as the LGW departures board shows RC411 at 14:25 but with a note 'Enquire Airline' in the status box. I recall that Atlantic were a target airline for SEN management a couple of years ago when they operated a weekly Vagar-Stansted service which has since ceased.
Last edited by Expressflight; 30th May 2016 at 09:06.