Forensic examination of postal votes cast for the extremist-linked mayor of Tower Hamlets, Lutfur Rahman, has shown that many appear to have been forged.

The evidence, from an independent forensic scientist agreed by Mr Rahman himself, will form the centrepiece of a rare election fraud trial opening at the High Court on Monday. Directly or through people working for him, Mr Rahman is accused of “corrupt and illegal practices” during his controversial re-election last May, including filling out other people’s ballot papers, ghost voting, ballot-paper tampering, smearing his Labour opponent as a racist, paying canvassers, intimidation and bribery.

Robert Radley, one of Britain’s foremost forensic document experts, has conducted electrostatic document analysis (Esda) tests on dozens of postal ballot papers marked with votes for Mr Rahman. The tests check for invisible indentations made on the paper from other documents written while resting on top of the document under investigation.

Mr Radley concluded that “none of the X impressions originated from other ballot papers within the same household,” proving that the ballot papers were filled in as part of an organised operation taking place at one or more central locations. According to other submissions in the case, many of the X impressions apparently match those on postal ballot papers allegedly stolen or taken from voters by supporters of Mr Rahman.

One of the suspect indentation marks was found on the ballot paper issued to Kabir Ahmed, a councillor who sought re-election for Mr Rahman’s Tower Hamlets First party. Mr Ahmed claims to live with his wife in a bedsit in Bethnal Green. The room is almost bare of personal touches and credit records show that Mr Ahmed in fact appears to live at an address in Ilford, outside the borough, though he says that this is the house of his parents-in-law.

Mr Radley also claims to have found that the inks of many of the entries “appeared very similar,” with a number of the ballot papers filled out in the same “distinctive and relatively unusual” ink. He also suggests that a number of the visible Xs were “similarly structured,” with a “very deliberate writing action, fairly precisely joining the opposite corners of the box.”

In their opening statement, ?seen ?by the Telegraph, the petitioners claim Mr Rahman has “a long history of abusing his power, inciting his supporters to intimidate his opponents, including through threats of violence, and corruptly funding organisations to promote him politically.” They will say he personally registered fake Labour Party members and voters, with “nine adult members of his family registered to vote” by 2012 at his terraced house in Spitalfields, many of whom had never lived there or moved out years before. The election, the petitioners say, involved “widespread and organised postal voting fraud” and ballot-paper tampering.

The petitioners will also say that a court-supervised scrutiny of the ballot papers, carried out last year as part of the case, found “a large number of ballots in which votes for other candidates were scribbled out or erased and replaced by votes cast for Lutfur Rahman”.

The petitioners will say that Mr Rahman’s campaign manager Alibor Choudury, a former activist in the IFE, told Bangladeshi voters that “Islam would only be safe” if Mr Rahman was re-elected and that his Labour opponent, John Biggs, “intended to close the mosques in the borough” if he won.

Investigations by this newspaper and the BBC’s Panorama have documented how Mr Rahman directed council grants and property sales to his religious and political allies, with funding skewed towards Muslim organisations and hundreds of thousands of pounds paid to bodies controlled by the IFE.

Mr Rahman also spent large sums of public money on promoting his re-election, with council staff employed at taxpayers’ expense to run his campaign and the chief reporter of a sympathetic local Bengali TV station handed more than £1,000 a week from council funds. An official newspaper promoting the mayor is distributed weekly to all homes in the borough, thousands of items of direct mail are sent to voters at public expense, illegal television adverts were run on local Bengali stations and large pictures of Mr Rahman were erected throughout Tower Hamlets.

The latest case, before an election judge, Richard Mawrey QC, is expected to last several weeks. It would normally be held in Tower Hamlets but has been moved to the High Court after persistent allegations that witnesses have been intimidated.

It is claimed that several witnesses who originally supported the petition have withdrawn their statements or given new ones diametrically contradicting their original testimony.