Sorting through things as you do, I came across two ten shilling notes from the 1960's, a 1960's issue pound note and a late 1940's issue pound note. They were not really in a collectors condition and had more or less been around the block a bit and served their time.
Each note had the line "I promise to pay the bearer on demand the sum of ..........,"
The notes had been out of circulation for years, so out of interest I thought I will test the system to see if I would be able to get the three pounds back which was the total value of the notes as promised by the Bank.
Looking on the Bank of England website I found a form to redeem withdrawn banknotes. So I filled it in and sent off the banknotes to the Bank in Threadneedle Street, London and waited.
Twenty four hours later a payment from the Bank of England ended up in my account. Not exactly a major financial transaction but the system certainly does work and a promise is a promise.