ANKARA (Reuters) - It will be impossible to tell how many unstamped ballots were accepted in Turkey's referendum to expand President Tayyip Erdogan's powers, or their impact on the tight result, because no records were kept, the head of the bar association said.
Sunday's referendum narrowly approved granting Erdogan sweeping authority over a NATO-member state which faces conflict on its southern borders and hosts 3 million refugees, making its stability vital to EU neighbours despite worsening relations.
Turkey's main opposition parties have called for the result to be annulled, arguing that the decision to accept unstamped voting papers was illegal and did away with a central safeguard against voting fraud.
Erdogan has dismissed complaints including a critical report from European observers. But Metin Feyzioglu, head of the Union of Turkish Bar Associations, said the decision had untold consequences that undermined the referendum.
"What makes any country a democracy is the security of the ballot boxes," Feyzioglu told Reuters in an interview. "Everything might be impeccable, but if your ballots are unsafe that means that regime is not a democracy."
Argument centres around a decision by the electoral board, two hours before polling booths closed, to accept votes on ballot papers that did not bear an official electoral stamp.
While foreign observers have said they did not witness specific cases of fraud, Feyzioglu said that decision meant the vote on the biggest overhaul of Turkish politics since the 1923 creation of the modern republic could have been manipulated.
"I cannot know whether there was cheating. And if so, who did this, was it organised, did everyone do it? I cannot know. You cannot know this either. Nobody can," said Feyzioglu, who is seen as a potential future leader of the main opposition CHP, which is appealing the outcome of the referendum.
"The only proof that (a ballot paper) has not been brought from outside is the timely stamping of the ballot sheet at the polling station," he said. "There is no other proof... If you use your imagination, you can write as many scenarios of irregularities as you want."
Once the ballot boxes were opened, officials at many voting stations stamped the unstamped papers in order to authenticate them, without recording details, he said.
"I believe this was with good intention... But it is in fact a crime, you cannot do that. You are validating a ballot sheet that should have been discarded," said Feyzioglu.
Standard procedure was for ballot papers to be stamped by officials at polling stations on Sunday morning before polls opened, to prevent anyone slipping in bogus papers that Feyzioglu said could be printed off at home.
He said the bar association had taken thousands of calls about unstamped ballot papers on the day of the vote, but it is now too late to calculate how many were affected.
"We cannot know the number... There was one way of knowing the number and that was keeping record of those that came out unstamped," he said.
Up to 2.5 million votes could have been manipulated - a number almost double the margin of Erdogan's victory, a member of the Council of Europe observer mission said on Tuesday.
Feyzioglu said the decision by the YSK election board came even though, in a ruling earlier in the day about which side of ballot slips should be stamped, it said "the aim of stamping envelopes is to prevent the use of fabricated envelopes".
Few people in Turkey expect a successful challenge to the referendum, which the YSK said was won by the "Yes" camp with 51.4 percent of the vote, according to preliminary figures.
However, Feyzioglu said that if the YSK rejected opposition appeals, the referendum could still be challenged in Turkey's Constitutional Court or at the European Court of Human Rights.
If the ECHR ruled that there had been infringements in the vote, the referendum would have to be held all over again, he said. "If you're carrying out such a big change to the system, one that impacts the regime, it must be without a doubt."
Additional reporting by Ece Toksabay; Editing by Dominic Evans/Mark Heinrich