Thanks, Richard Bridge, that's the one I want- half past. I was always hearing it in London. It seems to me that it should be half way to six rather than after.

Was McGrath trying to mislead me, or do Scots use it differently?

A quid is defined in the OED as a sovereign, a coin (skipping the early history) which, by Royal Proclamation, was defined as 20 shillngs in 1817. The origin is unknown.

(The game 'quidditch,' mentioned by Megan, above, is not cited in the OED. No such?)