Voting has begun in Burma on a controversial proposed constitution, as efforts to get aid through to cyclone victims continue.

The United Nations is expected to resume flights to Burma, which were halted on Friday after its World Food Programme announced initial deliveries had been seized by the Burmese regime.

The move comes as charities warn of a disease epidemic of “apocalyptic proportions” due to supplies not getting through to those in need.

Aid agencies have accused the country’s ruling junta of delaying crucial relief work needed to help the survivors of last Saturday’s cyclone that killed an estimated 100,000 people and has left some one million homeless.

UN secretary general Ban Ki-moon said his staff are negotiating with officials in Burma to break the deadlock, although he said leaders of the military junta have “regrettably” not yet made direct contact with him.

The military government has pushed ahead with a planned referendum although the balloting has been postponed for two weeks in the areas hit hardest by Cyclone Nargis - including the largest city, Rangoon.

The outcome of the vote is considered by many to be a foregone conclusion because the rules are skewed in favour of the military junta that has ruled since 1962.

Prime Minister Gordon Brown on Friday echoed the concerns of charities, stating that it was “unacceptable” that restrictions were being put on aid.

Mr Brown said the Burmese government “must take responsibility” for what is happening.

“We now believe that 100,000 are dead,” he said.

“It is completely unacceptable that the Burmese government should block the international aid.

“They should immediately remove the restrictions.”

His comments came as members of the Disasters Emergency Committee (DEC) said that they “could do more” if it were not for the opposition from the Burmese ruling junta.

Tim Costello, chief executive of World Vision Australia, said suspicion of foreign aid workers was hampering their work.

He said the Burmese government appeared concerned that aid personnel were foreign observers reporting on the constitutional referendum.

Mr Costello said the Burmese government did not have the capacity to run the relief effort required.

He said the affected area contains 19 million people and around two-thirds of them are children.

Mr Costello said: “The size of this is simply extraordinary and, in terms of its impact, much greater than the tsunami impact in Sri Lanka or Indonesia.

“The capacity to absorb this level of suffering, dislocation and chaos doesn’t exist (in Burma).

“It really requires international aid, it cannot be done in-country.”

The DEC appeal by British aid agencies and charities has raised £4 million in two days.