I posted recently on the film Lourdes, as it premiered at the Venice Film Festival (as far as I can tell, it was the world premiere, unless it had been shown at an earlier festival that I have missed).
The London Film Festival takes place from 14th October. It is a non-competitive festival, and shows a large number of films in cinemas across London. Films presented at the festival must be UK premieres, and English sub-titles are provided to films made in languages other than English. Most showings are open to the public, much like in any cinema. Each film that is presented at the Festival gets at least two screenings, with films anticipated to be more popular getting more.
Lourdes has two screenings, both at the British Film Institute/National Film Theatre on the South Bank. These are on Saturday 17th October at 21.00 (you can do Aid to the Church in Need's event at Westminster Cathedral in the day, dinner, and then on to Lourdes) and Tuesday 20th October at 13.00.
Online booking at http://www.bfi.org.uk/ (priority booking only today, open booking from Saturday).