AV debate: The voting system that Cameron is fighting for is a veritable novelty

Eton boys are taught history, one assumes. So although David Cameron's personal memories of British politics stretch back only as far as Margaret Thatcher's accession in 1979, he ought to have a basic grasp of how the British elections worked further back in time.

He very confidently invoked the wisdom of the centuries this week when he set out the case for a No vote in the coming referendum on electoral reform. Giving each voter "an equal say and an equal voice" is the "cornerstone of the British voting system", and the notion that it should be altered in any way is "unfair, it is wrong and it flies in the face of centuries of our history", he declared.

If we really are going to talk in terms of centuries, then the voting system Cameron and others are fighting to defend is a veritable novelty – younger, in fact, than Lord Reid of Cardowan, who appeared alongside the Prime Minister at last week's launch to assert that any voting system other than the one we now use would not be "British". John Reid was born in 1947. The first time the House of Commons was elected on the principles of what Cameron calls "an equal say and an equal voice" for all was in 1950.

Until less than 100 years ago, the people who ruled Britain would have thought it a very strange idea indeed than every Tom, Dick or Harry should cast a vote in a parliamentary election. To suggest that a woman could be trusted with a vote was downright subversive. No women were allowed to vote until 1918, and they did not gain parity with men until 1928.

The point of the House of Commons was to protect property owners from arbitrary rule by the monarch or the government. It was therefore natural that the interest of people who had a great deal of property counted for more than those who had owned only a little, and those without property did not count at all.

An MP's job was to represent a community rather than "the people" inhabiting it – a subtle distinction which meant that long-established communities could have one or two MPs even if their populations had declined, while places that had grown up suddenly during the industrial revolution had none.

Until the 1830s, it was common for a rich landowner to regard a Commons seat as his family property. These were the rotten boroughs and pocket boroughs, which had such tiny electorates that an election was easily bought or rigged. The families who owned them considered it their birthright to choose their MPs, or – if money was tight – to sell the privilege to someone else.

Old Sarum, site of the original Salisbury settlement, was the most notorious example. Because there was a bishop's house there in the 13th century, the area was invited by Edward II to send two representatives to the Commons. The bishop moved his residence to Salisbury soon afterwards, but for centuries, Old Sarum solemnly returned one or two MPs, long after its last human inhabitants had left. Only once in six centuries was there a contested election in Old Sarum, when three candidates vied for two seats.

Old Sarum held its elections under a designated tree in a cornfield. None of the electors lived in the constituency. No one did. But the landlord had the right to allocate votes to a handful of his tenants who would assemble under the tree and do as they were told.

The seat was owned by the Pitt family for 110 years, until they sold it for a reputed £43,000 after a member of the family had created a national scandal by instructing Old Sarum's seven electors to vote for a clergyman. It was considered improper for a man of the cloth to sit in the Commons. William Pitt the Elder began his political career under that famous tree.

Meanwhile Manchester was disenfranchised by Charles II as a punishment for its civil-war record, and remained without an MP for over 150 years. In 1819, a huge crowd which had gathered to demand representation for the city was charged by troops, leading to the so-called Peterloo Massacre.

These and other particularly blatant abuses were removed in 1832, by the first of three major Reform Acts passed during the 19th century. Yet some abuses slipped through. Midhurst, a rotten borough in Sussex owned by the Earl of Egremont, survived with one MP in place of two, and with widened boundaries which increased the electorate to 252. It disappeared during Queen Victoria's reign.

But up until 1950, the Commons was still a patchwork in which the principle of "one person, one vote" was not universally applied, and a candidate did not necessarily have to be "first past the post" to be elected.

Second past the post was good enough in middle-sized English towns such Blackburn, Bolton, Brighton, Derby, Norwich Oldham, Preston, Stockport, Sunderland and across much of Northern Ireland. These were all single seats which returned two MPs.

In most cases, the political parties put up two candidates in each seat, so if you were a Tory voter in Brighton, your vote was twice as important as that of your Tory neighbour's in Hove. But two-member seats did also facilitate deals between parties. In Dundee, where there was a strong Labour presence, the Tories and Liberals did a deal under which each put up only one candidate, successfully keeping the socialists at bay. The Liberal who benefited from this arrangement was Dingle Foot, the older brother of Michael, the Labour leader in the early 1980s.

The anomaly that seems strangest to us now is that universities elected MPs, separate from those representing the towns in which they were located – in contravention of that principle that everyone has "an equal say and an equal voice", which Mr Cameron seems to believe has is an age-old principle of our democracy.

University seats originated in Scotland, and were introduced to the Commons by James I of England when he took the English crown at the start of the 17th century. In the 20th century, Oxford and Cambridge Universities had two MPs each, London and Queen's, Belfast, had one each. The remaining English universities combined had two, the Welsh universities had one, and the combined Scottish universities had three.

AP Herbert is best remembered now as a satirist, whose Misleading Cases took the stuffing out of the British legal system. But he was also one of the MPs who almost single-handedly pushed through the Matrimonial Causes Act of 1937, which was a watershed in divorce law. But under the voting system as we now know, he would never have got into Parliament in the first place.

He was one of two MPs elected by Oxford University under a variation of AV. In 1935, there were four candidates for two seats, three flying party colours, and Herbert standing as an independent. Lord Hugh Cecil, son of a former Tory prime minister, topped the poll. The Labour candidate came last, and his second-preference votes were divvied up, with 1,342 going to Herbert and 177 to the other Tory. Herbert remained an MP until the constituency he represented was abolished.

The university constituencies which returned more than one MP all used the same variant of AV, which could produce the kind of result that would give No to AV stalwarts apoplexy. The Cambridge University contest in 1945 was particularly complicated, involving four counts. The Conservative candidate came first on every round, but there was an intense battle over who would claim the second seat. The writer JB Priestley, running as a progressive Independent, was ahead in the first three rounds, only to lose in round four.

The Labour government disposed of these university seats and of dual member seats in 1950, but that was only a tidying up operation. The pivotal year in parliamentary history was 1918, when the troops would soon be coming home from the war, Russia was in the throes of revolution and the British establishment wisely decided that the best way to avert civil upheaval was to alter the job of MPs so that they were at least nominally representatives of all the people.

The 1918 Representation of the People Act gave more than eight million the right to vote for the first time, and extended the franchise to every male over the age of 21. No sooner had the idea spread that the Commons was there to represent everyone, than a lively debate blew up about whether the first-past-the-post voting system was the best means of making sure that it happened.

There was a potential majority in parliament in favour of reform, but the reformers were divided between those who wanted proportional representation, who were concentrated in the House of Lords, and those who preferred AV. In the Commons, there was a ferocious anti-PR lobby led by the former Tory leader, Austen Chamberlain.

Eventually, the Commons voted 181-166 not to introduce the Alternative Vote system, and by a larger majority against PR. Just before the vote was taken, the prime minister, Andrew Bonar Law, at the head of a minority Conservative administration, admonished MPs in language that still has an unfortunate resonance: "I don't believe the country cares twopence one way or the other about either proportional representation or the alternative vote." What the public expected, he said, was that the politicians should make up their minds.