'Posh' an abbreviation of the French phrase 'poches profondes', meaning 'deep pockets'- a reference to wealth.

Well, actually, I just made that up. But it's as good as any other theory.

The practice of payment in notional guineas continues right to the end of the old coinage. A friend tells me that for her first job in an office in the mid 60s she was paid three guineas a week.

For a while after the introduction of the pound coin, they were sometimes referred to as 'maggies'- after Thatcher- they were brassy, hard, pretty worthless, and trying to pass themselves off as a sovereign.