The former US president Bill Clinton gave his support to the prime minister today, advising him to use his "big brain and good heart" to work through Britain's economic difficulties.

Clinton said he was not about to predict Gordon Brown's demise, and it would be "difficult to maintain a very high level of popularity" for any politician amid higher living and energy costs. Brown had to "trust the people" to "make a good judgment" whenever he decided to call a general election.

In an interview with the BBC Radio 4 Today programme, Clinton said he had known Brown for 20 years and was still in contact.

"I think anybody would find it difficult to maintain a very high level of popularity when average people are having the problems they are having today in the UK and the US with the soaring price of gasoline and the cost of living going up," Clinton said.

"I wouldn't predict Gordon's demise too quickly. I think he is just in a period where circumstances have got the British people appropriately concerned about how to get from day to day, week to week.

"The only advice I would give him is that he has got a big brain and a good heart - he just needs to apply them both to working through these issues as best he can and trust the politics.

"Just trust the people, at whatever time he stands for election, to make a good judgment. You get one of these jobs, the best politics is to do the job."

Clinton's comments came as he addressed an international Aids conference in Mexico City, where he called for more to be done to hold down the cost of anti-Aids drugs. He said a 50% funding rise was needed in the next two years just to keep pace with expanding drug programmes.

Clinton told the conference yesterday that his foundation would focus on fighting Aids in the US, especially in the black population.

He said he was spurred to action after the US centres for disease control reported that 40% more Americans had HIV than previously estimated. The report said nearly half of annual HIV infections in the US were among black people.

"For Americans, this should be a wake-up call," said Clinton. "Even as we keep working globally, we need to do much more to fight Aids at home, and I intend to do so with my foundation."

Clinton flew to Mexico after touring Africa to see the work of the William J Clinton Foundation's HIV/Aids Initiative.

The foundation has negotiated agreements to lower the price of rapid HIV tests and anti-Aids drugs in the developing world, and has collaborated with the Geneva-based Unitaid, a UN-backed fund that helps supply low-cost antiretroviral drugs.