Take the EUROSTAR train from the new St Pancras eurolink through the TUNNEL to Paris or Lille. From where the TGV ATLANTIQUE serves Lourdes five times daily from Lille Eurogare via Bordeaux or Montparnasse station.
There is also a nightly sleeper "couchette" from Paris Austerlitz. There is a bus connection from Lourdes station to Bareges.
London - Lourdes from £125 return. Book 2-3 months ahead to benefit from early booking discounts.