I could use a DVD recorder to record off digital satellite or cable. It wouldn't be as ideal as a pure digital capture (e.g. from someone with a Topfield box or DVB-T/S capture card), but connections are analogue RGB via SCART, so the quality would be reasonable.
Do you know during what programme the ad will be aired?
(Also, might be better to have someone else as back up, because I'm notoriosuly bad at remembering to record things...)