Very few people outside professional politics and the penumbra of SW1 read manifestos. Yet they matter: as Tim Bale notes, much of what they contain gets implemented in office. And just as importantly, their language and form tells you a lot about the nature of the politics of the moment.

The political language of manifestos has evolved with changes in the party system, the class structure and the nature of political leadership. The Liberal and Conservative manifestos of the Edwardian era were their leaders' personal addresses to their electors; they are patrician but petitioning, setting out the big issues on which the established political class was divided. The Liberal leader at the 1906 general election, Henry Campbell-Bannerman, was graciously solicitous: 'The dissolution of Parliament imposes upon you the duty of returning a representative to the new House of Commons, and I respectfully place my services at your disposal', he said to his constituents. Tory leader Arthur Balfour was equally polite: 'Such, in brief outline, are the public grounds on which I venture to recommend my candidature to your favourable consideration.'

In contrast, early Labour manifestos were published on behalf of the party rather than a leader. They are sharp, accusatory and insurgent, and infused with the urgent claims of their class. 'The great question you are to decide is whether the people or the peers are to rule this country', declared the first 1910 Labour Manifesto. '"The wealth for the wealth producers! Up with the people!'

A century later, all three main party manifestos bear the hallmarks of the professionalisation of politics, the decline of the class antagonisms of the industrial age, and the gravitation of parties away from civil society and towards the state. Contemporary manifestos set out programmes for government in temperate, often technocratic tones. They strive for responsibility and respectability. Today even Ukip, the most populist of all the UK parties, feels the need to have its manifesto audited. Like Ulysses tying himself to the mast, the parties supplicate the Office for Budget Responsibility to authenticate their fiscal rectitude and fitness to govern.

'The people' are an imagined, discursive category, liberally sprinkled across the pages of a manifesto, but rarely present as democratic participants in its development. Party leaders and their colleagues are increasingly drawn from a professionalised cadre; their manifestos speak the responsible language of office, and of constructed categories of voters – not the everyday language of their class or community interests. In 1910, the Labour party could declare that the country's problems demanded 'the attention of an active, determined and independent party, drawn from the people and in touch with the people'. Perhaps only the SNP, with its mass membership, could make such a claim today.

The expansion of the state and the centralisation of powers in Whitehall in the 20th century also expanded the range and reach of manifestos. Areas once deemed to be the remit of local government or civil society now come within the purview of the central state. So manifestos now contain long lists of policy commitments covering the waterfront of policy, and those of parties holding office and seeking re-election adumbrate almost everything a modern administration might do. Compare the insurgent arguments of the 1997 Labour manifesto with the checklist of targets and indicators it put before the people in 2001. Look past the garish colours of the 2015 Liberal Democrat manifesto and you will find a multitude of technocratic policy points that demand more of the reader than a public sector management consultant would dare ask.

Most often, manifestos betoken continuity as much as change. Even the transformative moments of British political history – 1906, 1945 and 1979 – were marked by deep continuities of culture and power. But, with hindsight, we know which manifestos were on the wrong side of history. Balfour could not convince the electorate to reject reform of the House of Lords in 1910, nor could Churchill convince the British people that, because their 'greatness had been built on character and daring, not on docility to a state machine', they should return him to office after victory in the second world war.

Sometimes, a manifesto glimpses towards the future, without knowing it does so. The 1979 Labour manifesto declared that 'free market ideas " are as dangerously out of their time as a penny farthing on the motorway'. Jim Callaghan knew otherwise. He told Bernard Donoghue, the head of the Number 10 Policy Unit, that a seachange was taking place in British politics, and there was nothing they could do about it. He was right. It was the postwar Keynesian settlement that was about to be consigned to history.

Within a fractured, multiparty system, in which no single party dominates, it is much harder to know whether an election is for an inter-regnum, or the opening up of a new economic and constitutional order. The rise of the SNP, the democratic energy unleashed by the independence referendum and the deepening demands for decentralisation in England signal a seismic shift in the territorial and constitutional configuration of the UK. Our relationship to Europe and wider geopolitical role may also be set fundamentally to change. And widespread anger at inequality and stagnant living standards may be the precursor to political economic reform. Time will tell.