The most significant change has been the increasing number of political interviews that now dominate the airwaves from early morning until late at night. The political landscape has been transformed by the expansion of daily current affairs outlets.
Relative newcomers include breakfast television, lengthier lunchtime bulletins, Channel Four News and Newsnight. They compete with the much greater emphasis being placed on politics from regular radio programmes such as Today and The World at One, now joined by Radio 5 Live. Then there are all the political programmes on a Sunday.
The endless round of political interviews sustains stories that would otherwise have faded away. One result is that whenever a politician is in trouble, he tends to stay in trouble for much longer. In the case of a prime minister in a period of political turbulence, the impact can be close to fatal.
There is a basic model: newspapers run a story about John Major's leadership crisis, sparked by an outburst from a critic - often Norman Lamont. Radio 4's Today team see the story in the first editions of the newspapers and get a reaction from another malcontent on the Conservative backbenches.
That is enough for The World at One to run a sequence which will include another Conservative rebel and a defence of Mr Major from a senior minister or the party chairman. The rush to defend the Prime Minister only heightens the air of crisis, though by this stage no one is quite sure what he is being defended from: there is just a sense of political volatility.
Channel Four News will have another minister defending Mr Major and firmly denying that there is a leadership crisis. At this point there is another important new element: newspaper correspondents wanting 'to move the story on' for the next day now have plenty of fresh, on-the-record quotes from the programmes to give their reports some substance. Before there were so many programmes it was harder to obtain so much decent, quotable material.
The impact of the political interviews can be seen in a comparison between Harold Wilson at his most vulnerable in 1968 and John Major since September 1992. The political interview, still something of an event in 1968, is now so commonplace that one feeds off another, renewing the sense of crisis. It is unlikely that Wilson would have survived in such an atmosphere. When Cecil King, chairman of the Daily Mirror, wrote a leader calling for his resignation, loyalists in the Commons organised a motion attacking King, but 77 Labour MPs did not sign it. Some were formidable opponents, but they did not have so many outlets to undermine their leader persistently. As a result, newspaper stories about the dangers facing Wilson petered out.
John Major was vulnerable during the forced withdrawal from the ERM and the battles over the Maastricht treaty, but reports of a leadership crisis have been more common since then. They began last September with an article in the Sun by Mr Lamont, in which he wrote: 'Given the right leadership, the British people could equal the best in the world.' The article was not as bitter as his Commons resignation speech, but it was strong stuff at the end of a summer recess, when there was little hard political news. It was enough to renew speculation about Mr Major's future, and to keep it on the front pages for the next six days.
The day after Mr Lamont's article, the Conservative MP John Carlisle spoke of the likelihood of a leadership contest, arguing: 'Even if the stalking horse was a one-eyed donkey it would not matter.' The quote made the front page of the Times. On the Sunday, Kenneth Clarke appeared on The World This Weekend to defend Mr Major, arguing that it was 'quite ridiculous to read that we are somehow plotting against each other or the Prime Minister . . .' although he went on to admit that the Government was 'still in a dreadful hole'.
Newspaper editors wondering how to continue the story for their Monday editions at least had a new top line - Clarke Backs Major As Leadership Crisis Grows. The quote was valuable in sustaining the momentum of a story in which the only fresh ingredient had been a Norman Lamont article many days earlier.
In January came the 'back to basics' furore. Just as it was seeming to die down the Sunday Times revived it by printing a front-page picture of Mr Major with his head in his hands, supported by a story about his troubles, based chiefly on unattributable quotes from senior Tory backbenchers. Nobody of any prominence was named.
The Sunday interview shows leapt into action. Sir Norman Fowler was summoned to The World at One to defend the Prime Minister, while Michael Mates, a former minister sympathetic to Mr Major, provided a useful quote for next day's papers about MPs' 'despair' at the succession of banana skins. Lord Tebbit also made the front pages by advising Mr Major, on Walden: 'You have got to make up your mind to decide where your friends are and where your policies should be and go for it.'
Last month another leadership crisis arose out of thin air and was sustained by the conveyor belt of weekend interviews. Michael Howard, the Home Secretary, went on the Saturday Today show to put on a bold face after the local elections and was asked about the possibility of a referendum on Europe. He did not rule it out. Then Kenneth Clarke was asked the same question on Sunday's The World This Weekend and put the anti-referendum case.
Suddenly, Conservative divisions over a referendum had become the main story. On the evening television bulletin the report said: 'In interviews today ministers failed to take a unified line on the question of a possible referendum on further European integration. Those on the right are clearly not ruling it out.'
Several broadsheet newspapers featured the story prominently on the Monday. The Today programme devoted several items to the issue. It included an interview with Mr Lamont, who had already said in his resignation statement that he supported a referendum on a single currency.
The World at One led with the referendum story. By Tuesday Mr Major's handling of the issue had become a key test of his leadership and was the main story in most newspapers. The impression was of a government falling to pieces, but the issue was utterly artificial. If Mr Howard had not agreed to go on Today, or if the interviewer had focussed on the economy, it would never have arisen.
In the spring of 1968 Harold Wilson had lost a foreign secretary, was being fairly openly conspired against and faced a hostile press. In some ways he was in greater danger than John Major, who enjoys the support of a loyal foreign secretary and has a chancellor whose leadership ambitions have been temporarily thwarted because of the tax increases.
But there was not the sustained coverage highlighting his vulnerabilty as there is with Mr Major. The media will ensure that there is nowhere to hide, no rest from the public assessment of his weaknesses. It will need a much greater act of will to withstand such an assault.
Steve Richards, a BBC political correspondent, is researching changing patterns of political reporting as a Reuter's Fellow at Oxford.
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