How many pennies in 50p?
Not so any more. They have introduced charges to the busiest ones (=the ones they can get away with stiffing the tourists, around St Pauls and the Tower of London) and it is not clear if they will introduce them to the rest, such as this one in Smithfield. So now, it costs 50p to spend a penny. The expression comes from the old Public Lavatories that used to be coin operated, they cost 1d - old penny - or less than 0.5p now.