More pressure must be piled on the Sudanese government after new evidence showed security forces storming a Darfur refugee camp, says Jack Straw.
BBC footage shows tear gas being thrown at refugees
Responding to a BBC film which also showed civilians driven away by officials, the foreign secretary said he found the footage "very shocking".
"I hope this alerts the international community to the scale of the problem."
Sudan's ambassador in London played down the incident, saying troops were trying to move people to a better camp.
Hassan Abedin said force was used only on a small number who were trying to incite resistance to moving from the camp.
"Yes, I would say there were incidents of police... mishandling some individuals, but the idea is to enable the... vast majority of the people in this camp to move to a better camp," he said.
But BBC correspondent Fergal Keane said he witnessed police fire tear gas and assault residents at the el-Geer camp near Nyala, just hours before the UN's Sudan envoy arrived at the settlement.
Government forces staged two assaults on displaced people, and would not desist from bulldozing their camp, despite the presence of UN representatives, the African Union and international aid agencies.
At one stage a plastic bullet was fired at a BBC cameraman standing next to a UN vehicle.
Tear gas was fired at people, mostly women and children, queuing at a nearby medical clinic.
A police commander at the scene told the BBC's correspondent that he was under orders to move the people to a new camp several kilometres away.
Responding, Jack Straw said he hoped the "concrete evidence" would be broadcast in the capitals of Security Council members, "who frankly have thought that it is time to slacken our efforts in Sudan, rather than increase the pressure".
BBC correspondent Bridget Kendall said the UK government was concerned about the rise in levels of violence. Particularly, she said, evidence of "relocation", just a day after the government and the rebels signed what has been described as a breakthrough agreement aimed at ending the crisis.
Mr Straw believes diplomatic language should now be toughened up, she said.
It comes as the Security Council prepares to meet away from its usual New York base, in the Kenyan capital Nairobi for a special session on Sudan.
Sudan though has accused the international community of overplaying the security crisis in Darfur.
A police action at the camp last week was condemned by UN Secretary General Kofi Annan.
The UN has condemned the relocation programme, calling it a breach of humanitarian law.
Some 1.6 million people have fled their homes and tens of thousands have lost their lives in the conflict in Darfur.
Pro-government Janjaweed militias are accused of driving the region's black Africans from their villages, since two rebel groups began an uprising in February 2003.