Yes it's Leftfield, I think it's Release The Pressure from the album Letfism. I'm not sure it's necessarily the band selling out. Depending on what sort of contractual arrangements exist, the record company sometimes can allow use of a song without having to get the artist's agreement.
Two things stick in my mind from that ad. 1. The cheese string looks revolting and why the f*** would anyone want to ingest such sh*t. 2. That boy is a smug little git who needs a right slapping.