Whilst pounds were the denomination, for much of the nineteenth century they were not readily available as a piece of currency. Bank notes were essentially cheques, in the early days payable to a specific named recipient. It was 1855 before bank notes were machine printed and payable to 'the bearer', and therefore available to everyone. However issues of bank notes were limited because of a lack of gold to back up their value. In 1826 notes of less than five pounds were banned, it was probably 1844 before lesser notes were issued. The wording on the note says that the 'Chief Cashier of the Bank of England (other banks are available) promises to pay the bearer the sum of one pound', in other words, they will let you have enough gold equal to the sum of one pound. The coin which reprented this value was the gold sovereign.....These became generally available after 1821 when they were issued to represent a coin valued at a pound, rather than the guinea (£1, 1shilling in value), that had been in circulation before that time (guineas were intended to be withdrawn). Whilst these were useful coins there was some unwillingness to receive them...they were often 'clipped', i.e. shavings of gold were taken off the coins to get some cash for the gold scrap. People (and banks) went to the trouble of weighing every sovereign to check it was the correct weight. Short weight meant that the payer had to make up the shortage with other coins to pay the bill.
Sovereigns continued in circulation until the first world war when they started to be withdrawn to bolster our gold reserves, and many more notes were put into circulation.
The rest of the UK coinage was silver (sterling silver of course! This dropped to 50% silver after 1920, and none after 1947 when coins became cupro-nickel.), and the small change in copper (brass after 1860), these were less prone to clipping.