Before the Reform Act of 1832 there was no uniformity in the distribution of English parliamentary constituencies. By the 1780s, in Cornwall and Devon, 1050 people voted for 53 MPs but growing northern industrial towns had no representation. For example, in 1831, Manchester had a population of a quarter of a million but no representation in parliament. Each county had two MPs, regardless of the size of the county.
There were two types of MP:
County MPs had to own land worth £600 p.a. and usually were from the great landed families of the country;
Borough MPs had to own land worth £300 p.a. Often they were local squires, landed gentry or the sons of the aristocracy.
For the County Franchise, each elector had to own land worth 40 shillings, freehold. This had been a national standard since 1429/30 but because of devaluation and increased wealth, the number of electors had increased. Also, if a man was a tenant of land worth 40 shillings freehold, he was allowed to vote. This meant that many tenant farmers had to vote the way the landowner told them.
The Borough Franchise had no uniformity whatsoever because the system had grown haphazardly. There were 203 boroughs with 402 MPs between them.
There were a number of different types of borough franchises. Old Sarum was a Burgage borough, of which many became known as 'Pocket Boroughs' because one person would buy the majority of the burgages in the locality. (Expression "He has it in his pocket" = has total control.)
In 1691 Thomas Pitt bought the Manor of Stratford and Old Sarum for £1,000 from the Trustees of James Cecil, 4th Earl of Salisbury, and thus obtained control of this nomination/burgage borough of Old Sarum. Other members of the Pitt family later held the seat, most notable William Pitt, (the Elder) Lord Chatham, who became Prime Minister of England in 1766.
Voting took place under an ancient tree (variously described as an oak or an elm) situated on the southern slopes of Old Sarum. The tree became known as The Parliament Tree and survived until 1902. A commemorative board mounted on a sarsen stone can be found adjacent to a footpath between The Portway and Castle Road and marks what is believed to have been the site of the tree.
The Parliamentary Reform Act of 1832 disenfranchised Old Sarum but its reputation lives on.
As recently as 2007, Old Sarum was mentioned in the House of Lords by Lord Avebury:
"Before 1832, there were the rotten boroughs, of which perhaps the most notorious was Old Sarum in Wiltshire "
www.historyhome.co.uk/c-eight/constitu/parlrep.htm accessed 5 April 2017
www.en.wikipedia.org/wiki/Rotten_and_pocket_boroughs Accessed 5 April 2017
www.parliament.uk accessed 5 April 2017
www.publications.parliament.uk/pa/ld200607/ldhansrd/text/70518-0003.htm Accessed 5 April 2017