The penny was originally one 'pennyweight[?]'. A pennyweight is a unit of mass which is the same as 1.555 grams, or 1/240th of a troy pound. So, a penny was literally, as well as monitarily, 1/240th of a troy pound of sterling silver. The weight of this coin was instituted by Charlemagne, and the purity of 92.5% silver (sterling silver) was instituted by Henry II in 1158 with the "Tealby Penny" -- a hammered coin. At this time the standard unit of currency in England was the penny.
The medieval penny would have been the equivalent of around 1s 6d in value in 1915. British government sources suggest that prices have risen over 61 fold since 1914, so a medieval sterling silver penny might be worth around £4.50 today, and a farthing (a quarter penny) would have the value of slightly more than today's pound. Inflation has eroded currency value by that much.
Since carrying around a lot of precious metal was cumbersome, banknotes were issued. Banknotes were originally a claim to an amount of precious metal stored in a vault somewhere. In this way the stored value (usually in gold or silver coins) backing the banknote could transfer ownership in exchange for goods or services. So long as each circulating banknote was backed by the appropriate amount of metal the storage and representation of the stored metal constituted the 100% reserve banking system, and the currency system is one based on specie money[?], which takes the forms of commodity money or representative money because it is backed by something of intrinsic value.
Today banknotes are not backed by any intrinsic value. Circulating banknotes are not backed by any reserve of value, but only on the faith that the paper will be honored when it is offered to pay for goods or services. A £100 note is no harder to produce than a £1 note, so the £100 note does not represent any greater intrinsic value than the £1 note. The currency system we currently use is one based on fiat money.
Sterling banknotes are issued by the Bank of England in England, the Bank of Scotland[?], Royal Bank of Scotland[?], and the Clydesdale Bank[?] in Scotland and by the Bank of Ireland[?], Northern Bank[?] and Ulster Bank[?] in Northern Ireland, also by the Government of the Isle of Man and the States of Jersey and Guernsey.
All the notes also depict Elizabeth II of the United Kingdom.
Bank of Scotland banknotes in circulation are:
All the notes also depict Sir Walter Scott who was instrumental in retaining the right of Scottish banks to issue their own notes in the 1840s.
Royal Bank of Scotland banknotes in circulation are:
All the notes also depict Lord Ilay (1682-1761), first governor of the bank.
Clydesdale Bank notes in circulation are:
Also see British coinage.