This week's revelation of unlawful donations to the Labour Party is the latest in a series of scandals to befall the Government. History shows that the odds are against long-term prime-ministers-in-waiting, but could commentators be writing Gordon Brown's political obituary too soon?

I doubt whether the Prime Minister and the Prince of Wales have ever spent much time in each other's company. Yet if they did and the conversation turned to their mutual predicaments, the degree of similarity which they might recognise would be considerable.

Whether it be monarchy or democracy, waiting in the wings for a prolonged period of time is frustrating and appears to have an impact on behaviour and character. Prince Charles' somewhat wayward private life seems to have followed the path of others such as George IV, Edward VII and, most notoriously, Edward VIII, who all served as the heir to the throne for what must have seemed to them to be an eternity. When they ultimately succeeded it was too late for them to make much of an impression. One can only hope for the present Prince of Wales that history does not repeat itself cruelly.

Gordon Brown is in a similar situation. The record of prime ministers who arrived in Downing Street after predecessors of the same party who served long and notable terms is, superficially at least, rather dispiriting. The Earl of Rosebery took over from William Gladstone but was ejected from office a year later. Arthur Balfour assumed power from the Marquis of Salisbury but endured a torrid time and suffered a landslide defeat in the 1906 election. Neville Chamberlain's tenure after Stanley Baldwin was a disaster. Anthony Eden cashed in his electoral chips shortly after replacing Winston Churchill but would be obliged to resign little more than 18 months later. John Major secured a mandate of his own after succeeding Margaret Thatcher but that was virtually the sole bright spot for him during a period which must have felt like torture and ended in ignominy.

Nor it is difficult to understand why these fates might occur with such consistency. It is hard for the new man to step out of the vast shadow cast by their predecessor. The agenda of the political party concerned has, inevitably, largely been exhausted by the moment that the incoming prime minister is finally elevated. The passage of the years ensures that the four words, "time for a change" become almost a self-fulfilling prophecy.

After the events of the past month it is tempting to contend that Mr Brown has little chance of avoiding the political misery of others in his position. He started strongly enough, benefiting from the sense that Tony Blair had delayed his departure for too long, and acted deftly when confronted with a wave of crises and incidents for which he could not be blamed and where a reassuring response was required. Then came his decision to allow speculation about, and preparations for, early hustings on 1 November to run out of hand and have to be abandoned in an extremely embarrassing fashion.

Since then it has all been downhill with Ministers apparently under siege, courtesy of their inability to count immigration figures correctly, the fear that the bailed-out Northern Rock might prove a huge burden on taxpayers for far longer than anticipated, and the astonishing complacency and incompetence that allowed Her Majesty's Revenue and Customs to mislay computer discs with the private details of 25 million people on them.

Other developments, such as the Labour Party accepting illegal donations, have hardly helped either. The fact that the businessman David Abrahams gave Labour more than £650,000 using the names of four other people has been described by Mr Brown himself as unlawful and completely unacceptable.

All of which has been compounded by adverse comments about the Prime Minister personally. After a few weeks in which it was thought that the sheer liberation of entering Number 10 had produced a "new Brown", the consensus is that the "old Brown", the reclusive creature surrounded by a small cabal of acolytes when at the Treasury, has reasserted himself.

Jackie Ashley, a strong sympathiser, wrote in The Guardian on Monday of the compelling need for the "Good Gordon" to drive out the "Bad Gordon" for him to be able to prosper. When your friends are discussing your personality in terms that resemble Dr Jekyll and Mr Hyde, then you appreciate that person is really in quite considerable trouble.

History is not, however, the set of handcuffs or ball and chain that it might seem for the Prime Minister. There are three reasons for him to have faith that some of the obituaries being written for him might yet transpire to be wildly exaggerated.

The first is that he has a lot of time in front of him. The next general election does not have to be held until June 2010, which is a considerable distance. The outcome for administrations that defer polling day much beyond four years is, admittedly, not a stellar one but there are important exceptions, notably October 1959 and April 1992. Labour's majority in the House of Commons is far too large for it to be endangered even by a string of by-election defeats; and these contests are becoming less frequent anyway (if nothing else, the reform of parliamentary hours and conditions in the past decade has made MPs, collectively, more robust in health than they used to be).

By 2009 or 2010, migration figures and lost computer records will almost certainly have been forgotten (whether Northern Rock has repaid the Bank of England in full is more debatable). I also suspect that the Prime Minister will have acknowledged some of the criticism of his management style well before then too and will have expanded his unduly small inner circle.

The second reason is the unpredictable nature of the economic outlook might work in his favour. Opinion polls indicate that voters are much more pessimistic about their prosperity over the next 12-18 months than most of the financial experts would deem rational. There is the danger, of course, that consumers will be the catalyst for a recession, which would not otherwise have happened, by cutting back their spending suddenly and savagely. The key to the condition of the economy, nonetheless, is whether the "credit crunch" rooted in the United States spreads sickness elsewhere.

There is obviously a chance that it will but, equally, the United States Federal Reserve Bank has already shown itself prepared to slash interest rates there aggressively to avoid a financial meltdown. If it continues to do so in 2008 then the Bank of England would find itself emulating that same strategy - regardless of its Governor's distaste for the "moral hazard" of bailing out bad bankers. If Mr Brown is seen as having navigated these choppy waters it will reflect well on him.

Finally, there is another interpretation available as to why Rosebery, Balfour, Chamberlain, Eden and Major were all such ineffective prime ministers. It is that they were destroyed not by their inheritance but by a series of issues, mostly related to foreign policy (intriguingly), which brutally split their political party. These were Home Rule for Ireland, Imperial Preference, Appeasement, the Suez Crisis and Europe. According to this theory, it takes truly devastating episodes on this sort of scale to overwhelm an administration that is otherwise in reasonable condition. Iraq might have been such a spark for new Labour's demise if the Conservative Party had opposed that conflict. It is not evident that Mr Brown will have to endure such an epic controversy.

With the exception of the highly volatile 1920s and 1970s, the pattern of British electoral history is of a dominant party that is only defeated once it has itself imploded. If so, then familiarity does not necessarily always breed contempt from the electorate. Hence the ironic conclusion is that the son of the manse must pray that "The devil you know", not "Time for a change", are the four most important words in politics.