Protesters from Sussex scaled a crane in a backlash against Cabinet ministers associating themselves with the Make Poverty History campaign.
Leila Deen, 25, Kath Pasteur, 34, and Paul Hutchings, 37, of the Brighton branch of the World Development Movement, scaled the 150ft structure to unfurl a banner at first light in Edinburgh today.
Speaking from the top of the crane, Ms Deen, of Lower Rock Gardens, Brighton, said she had been angered to see Chancellor Gordon Brown and International Development Secretary Hilary Benn taking part in Saturday's march in Edinburgh.
The University of Sussex student said: "We had not been planning this but we were so upset by their participation that we decided we had to do something.
"We felt it was urgent on behalf of all the thousands of people who marched to make it clear the Government is not part of the Make Poverty History movement. The department for international development is actually making policies which go against the movement.
"One minute it says it is onboard and the next it is ignoring unjust trade rules."
The three walked past security guards and climbed a ladder in the crane at Edinburgh's Waverley station without safety equipment.
They carried bicycle locks to chain themselves to the crane and dangled a banner which read: "No more Brownwash", from the side of the structure.
Ms Deen said: "It was almost completely unguarded. We got past two workmen who were drinking a cup of tea, hopped over a fence and we were there. It was surprisingly easy."
On the ground, police officers talked to other members of the movement while the protesters insisted they would stay until their point had been made.
Ms Deen told The Argus this morning: "We have been up here for about three hours and are waiting to see if the police tell us to come down.
"It is quite scary being so high up but not as scary as the way Brown and Benn are managing to dominate the Make Poverty History campaign.
We will stay up here until we have got our message across and clip ourselves on if we need to."
University researcher Ms Pasteur, 34, of Steine Street, Brighton, said: "While Gordon Brown claims allegiance to the movement he has chosen to ignore the most important demand of the campaign.
"Rebalancing trade rules to favour the poor is the structural change needed to allow countries to develop on their own terms."
The three are part of a 17-strong group from Brighton and Hove who have travelled to the city for the G8 summit.
They are among thousands of protesters hoping world leaders will commit themselves to ending poverty in the developing world when they meet at Gleneagles tomorrow.
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