Brown will pledge to stand by Israel and condemn threats against the country by Iranian President Mahmoud Ahmadinejad, according to excerpts of the speech released by his office in advance.
"Iran now has a clear choice to make: suspend its nuclear programme and accept our offer of negotiations or face growing isolation and the collective response not of one nation but of many nations," Brown will say.
"Just as we have led the work on three mandatory sanctions resolutions of the United Nations, the UK will continue to lead -- with the U.S. and our European Union partners -- in our determination to prevent an Iranian nuclear weapons programme," Brown said in the excerpts.
The United States, Britain, France, Germany, Russia and China have offered Iran financial and diplomatic incentives to halt nuclear activity which the West fears is a cover for making bombs. Tehran says it is aimed solely at generating electricity.
After talks in Geneva ended in stalemate on Saturday, six major powers gave the Iran two weeks to answer calls to rein in its nuclear activities or face tougher sanctions.
British government officials travelling with Brown said if Iran did not accept the incentives, the next step would be to ratchet up sanctions against Tehran, possibly including sanctions on Iran's oil and gas industry.
They said such sanctions could seek to target Iran's domestic energy market by making it difficult for Iran to obtain equipment and spare parts for its refineries.
Tensions between Iran and the West have helped drive up crude oil prices to record highs in recent months.
BRITAIN TO STAND BY ISRAEL
Calling Ahmadinejad's 2005 statement that Israel should be wiped off the map "totally abhorrent", Brown will say in the speech: "To those who question Israel's very right to exist, and threaten the lives of its citizens through terror, we say: the people of Israel have a right to live here, to live freely and to live in security."
Britain will stand beside Israel "whenever your peace, your stability and your existence are under threat," he will say.
Speaking to reporters on Sunday evening, Brown said Iran had broken the terms of the nuclear Non-Proliferation Treaty and had "misled the international community about the scale of their preparations for weaponry."
The United States has refused to rule out military action against Iran if diplomacy fails to resolve the nuclear row.
Israel, long assumed to have nuclear arms, has sworn to prevent Iran from obtaining atomic weapons. An Israeli air force drill last month raised speculation it was planning an attack.
A senior Iranian official was quoted this month as saying Iran would destroy Israel and 32 U.S. military bases in the Middle East if the Islamic Republic was attacked.
