Some of the most turbulent and memorable events in the history of Conservatism had their origins in Birmingham, the great city where once the Chamberlain family reigned. The Liberal Unionist movement was born here, before it fused with the Tory party. The tariff reformers held their great meetings here, splitting the Conservatives for decades. Here the alliance between Tories and industry was forged and a gritty municipal Conservatism first found its voice.

So if the Tories had come to Birmingham for a smooth self-congratulatory conference, it would have been out of keeping with the party's history in this city. But economic turmoil will test the party once again. David Cameron has thrived in the boom, promising to safeguard public services and tackle social breakdown. A slowing economy means that a Conservative government will have less money for both. Compassionate Conservatism is a more difficult proposition in a recession.

Mr Cameron's leadership has, so far, been a success. He has led his party from the front, making it more modern and more sympathetic. He wears the pressures of political life with a remarkable ease, he has maintained strong party discipline and he has earned, for now, the united support of the Conservatives. While swing voters are still unsure about his party, they warm to Mr Cameron himself.

One element in his success has been what has become known as the “sunshine strategy”. Even though Mr Cameron has sometimes used jarringly pessimistic language - for instance, his assertion that “society is broken” - optimism has been a mark of his leadership. Even his dire analysis of social breakdown has been married to an upbeat confidence that something can be done. Family breakdown, knife crime, obesity, the worrying discounting of confectionery at the wrong till - Cameron's Conservatives have been confident they could fix things, turn black skies into blue ones. Yet this optimism depended on a strong economy. Mr Cameron claimed that he would mend the broken society as Margaret Thatcher mended the broken economy. Now the economy is in need of further repair.

Mr Cameron's first problem will be to avoid being eclipsed. When banks are failing and the US Treasury Secretary is crawling around on his knees, Prime Ministers are in their element. They can act. All the Leader of the Opposition can do is talk. Mr Cameron has a strong point to make - that current difficulties are partly of this administration's making - but he may find it difficult getting that point heard. Another strategic difficulty will be finding ways to retain his appeal as a new kind of Tory while delivering traditional tough Conservative economic messages.

However, the more serious challenge posed by economic conditions will be to his detailed plans for change. Reform of public services is often written about as if it saved money. In truth, in its early years change will cost money. Will Conservative reforms of education and welfare - central parts of Mr Cameron's platform - still be affordable with the Tory leader insisting (correctly) that his first priority is to reduce debt?

Mr Cameron insists that he intends to keep the trend rate of growth of public spending below the trend rate of growth of the economy. Yet the costs of maintaining the NHS on its current principles will be rising faster than that. In the 1980s the Conservatives simply suppressed health spending, a policy that worked for a period but required correction by the end of the 1990s. If the Conservatives have a more imaginative strategy than simple suppression of spending, they have yet to unveil it.

Mr Cameron fixed the Conservative Party while the sun was shining. It remains to be seen how well he will do in a colder climate.