Open Water was on the telly last night (ITV2 9.00), a film based on real events, apparently. Two young scuba divers surface from a jolly to find the dive boat, having made a faulty head count, has sped off back to port leaving them out at sea.

They work out – very early on – that they are drifting north (at least to the left on TV) in an ocean current. After a night at sea they spot a beacon a mile or two away.

That is when you or I, dear reader, would have swum about due east to make sure we were on the same longitude as the beacon , then let the tide take us down on to it.

These two, don’t.