Viktor Yushchenko will never recover his good looks after his near-fatal poisoning with dioxin, Times Online has learned today.

The British pathologist who first suggested that the Ukrainian opposition leader had been poisoned with the rare toxin also revealed that Mr Yushchenko's facial disfigurement will probably get much worse before it starts to improve.

Professor John Henry, who works at St Mary's Hospital in Paddington, West London, said that the dioxin dose received by Mr Yushchenko could easily have killed him.

He spoke as a much-anticipated television debate between the two bitter rivals got under way with Mr Yushchenko accusing his rival of trying to steal the November election..

"(The disfigurement) may get steadily worse, it's worse every time you see a picture him," Dr Henry told Times Online of Mr Yushchenko's pock-marked appearance.

"It may get worse before it gets better. I think he will be disfigured for at least two to three years, and he will not recover the good looks and clear skin that he obviously had."

The only other victim known to have received a similar dose suffered an eruption of skin cysts all over her body that grew worse and worse for a year after the poisoning, until the condition eventually started to ease.

Mr Yushchenko, a former prime minister and central bank chief, accused his political opponents of poisoning him after falling severely ill on September 6, during campaigning for the Ukrainian presidency. His face is now covered in cysts and appears an unhealthy green colour.

The opposition leader is favourite to win a repeat of the presidential run-off vote on Sunday, called by the Ukrainian Supreme Court after it decided that the first run-off had been stolen by Viktor Yanukovych, the Prime Minister, through vote-rigging.

Tonight the two rivals stood facing each other for the first time in over a month, in a blue television studio. Mr Yushchenko, wearing a tie in his campaign color of orange, spoke first, saying the reason for the Boxing Day election rerun "was that the results of the November 21 votes were stolen ... by my opponent and his team".

In his introductory remarks, Mr Yanukovych, wearing a tie in his trademark blue, spoke in Russian instead of Ukrainian. "Your accusations toward me and toward my voters don’t give us the chance to look into the future optimistically," he said, wagging his finger.

Rules for the 100-minute debate allow the two candidates to ask each other questions directly after first giving their opening statements. Ukrainians crammed into cafes and restaurants to watch the first debate in November, and even more were expected to tune today. Foreign policy, the economy and social benefits were expected to dominate, but the poisoning allegations were also expected to surface.

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