Brown, whose country is the former colonial power in Zimbabwe, said he had explained Britain’s position to Morgan Tsvangirai, who was sworn in as prime minister of a unity government on Wednesday.
"I said to him that we would want to see humanitarian aid getting to people who are in a distressed position," he told lawmakers.
"But I also said … that until the government of Zimbabwe could convince us that there were going to be free and fair elections, and at the same time that there was going to be the removal of repressive legislation … until these things happened, we could not treat Zimbabwe as if it was an ordinary country."
He added: "I hope there will be considerable pressure by the international community to release political prisoners, to get in a credible team to deal with the finances, to have a clear roadmap to the next elections.
"These are the indicators of change that we will be looking for."
But he warned: "I fear that President Mugabe will still stand in the way of these changes."
His comments came as Tsvangirai set to work to bring his top aides into Cabinet posts where they will have to strike a delicate balance with their erstwhile adversaries.
Mugabe has yet to announce his appointments for ministries set aside for his Zanu-PF party, but the new government already seems certain to create strange bedfellows: Tsvangirai has named deputy ministers who will have to work with Mugabe’s choices on the defence, agriculture and foreign affairs portfolios.