LIVE 8 today steps up the pressure on the G8 leaders ahead of their summit in Edinburgh next week with a warning that failure to secure an “historic breakthrough” at Gleneagles would be a betrayal of the world’s poor.

In an open letter published by The Times, the organisers behind today’s ten rock concerts around the world, including Bob Geldof, Bono and Richard Curtis, say that they have created a mandate for action against the poverty that is killing 50,000 people a day:

“We will not applaud half-measures, or politics as usual. Don’t disappoint us. Do not create a generation of cynics. Do not betray the desires of billions and the hopes of the poorest of our world.”

Fears that the summit will end in inconclusive compromises prompted a show of defiance from Tony Blair yesterday. The Prime Minister intends to play a game of “brinkmanship” in negotiations over aid and trade, as well as climate change.

Downing Street last night indicated that the prospect of pre-summit deals being agreed between officials from G8 nations this weekend was unlikely. “We will push it to the wire at Gleneagles itself if that is necessary, because we want to squeeze as much out of this as we can,” a spokesman said.

Although ministers are keen to ensure that expectations of what can be achieved next week are realistic, they are also stressing that the Government is pursuing a “high-risk strategy” in talks with the United States, Russia and others.

This robust message last night was in stark contrast to the growing pessimism over the summit among charities and pressure groups.

In the latest leak from the draft communiqué facing G8 leaders at Gleneagles, The Times has learnt that plans for a new agreement on international arms sales have been watered down. The text is understood to make no mention of a legally-binding treaty — referring instead to “principles” — while also limiting its scope to small arms.

An international arms trade treaty was one of the key recommendations from Mr Blair’s Commission for Africa report this year. But Jack Straw, the Foreign Secretary, has made little headway in negotiations with arms exporters such as Russia in recent months.

Tidjane Thiam, a former Minister in the Ivory Coast and one of the 17 Commissioners behind the report, said: “This will be very disappointing. There is no point talking about giving more aid to Africa if the money is going to a war zone — where most of the weapons are made in G8 countries.”

Oxfam yesterday also raised concerns over another recommendation from the Africa Commission which called for an additional $25 billion of aid for the continent — a sum described by Live 8 today as the “absolute minimum required”.

Although ministers believe that they are close to securing the $25 billion, along with a similar sum for other developing nations, the money is unlikely to be available until 2010.

Jo Leadbeater, Oxfam’s head of advocacy, said: “The last thing Africa needs is a fudge, delaying the $50 billion increase. The black hole that will open up in the intervening period is a massive $100 billion.

“Every cent of that is money that could have saved the lives of the world’s poorest people. 2010 will be five years too late for the 55 million children who will die waiting for the world’s richest leaders to deliver on their promises.”

Britain is confident of finalising a $40 billion debt cancellation deal for poor countries, but accepts that progress on removing trade barriers may be delayed until later this year.

The Government wants to wipe out global farm export subsidies by 2010 to help Africa to trade its way out of poverty. Talks on this were yesterday said to be “tough” but The Times understands that Gordon Brown is pushing at least for a declaration of intent. Such a statement would give a huge boost to the next World Trade Organisation talks in Hong Kong this year.

But Mr Blair has been unable to overcome opposition from President Bush in his pursuit of an international action plan on climate change because the US refuses to accept that burning fossil fuels is causing global warming. Instead, Britain may use Mr Bush’s concerns over the security of oil supplies to get agreement on subsidising renewable energy.

The leaders of China, India, Brazil, Mexico, South Africa and India are also being invited to share round-table discussions with the US at Gleneagles about “co-ordinated measures” for moving towards a low carbon economy.

The Prime Minister will not attend today’s London Live 8 concert in Hyde Park, where the Government is likely to be represented by Tessa Jowell, the Culture Secretary. He has told friends that, while Britain’s presidency of the G8 “will not save the world, it may be seen as having made a start”.

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