A forensic handwriting and document examiner said a large number of ballot papers from last year’s Tower Hamlet’s mayoral election could have been filled out with the same pen and many seemed to contain the same handwriting.

The Royal Courts of Justice, where Mayor Lutfur Rahman has been accused by four petitioners of a number of indiscretions including orchestrating voter fraud, also heard there were discrepancies noticed within different parts of the same postal vote ballots.

In his witness statement Robert Radley from The Radley Forensic Document Laboratory, who tested a batch of the votes for the trial, said a large number of 'x' marks on the voter forms could be divided into a“relatively small number of specific groups of inks”.

“Consequently there has to be a very high level of coincidence for such numbers of indistinguishable inks to appear,” added Mr Radley, who was said to have tested more than 80 papers for the case.

The witness added he had tested "many hundreds of ballot papers" in a variety of cases over the last 37 years.

"I do not recall this particular feature in such quantities in previous cases, especially when one considers that this feature is found in approximately 25% of ballot papers for one ward (Weavers Ward). For this to happen by chance would, in my opinion, have to be a very considerable coincidence.”

However, during cross-examination by Duncan Penny QC, representing the mayor, Mr Radley admitted he had no statistics on the use of particular inks in Tower Hamlets.

Regarding the suggestion some postal vote ballots had different handwriting contained within them, the expert witness said: "It's extremely unusual for someone to sign their name poorly but write letters well."

The hearing is expected to run until Friday. Richard Mawrey QC, who is sitting as a judge in the case, is expected to reach a ruling after Easter.

If he finds against Mayor Rahman, last May's election could be declared void.