An east London mayor has been removed from office and a poll declared void after he was found guilty of electoral fraud.
An Election Commissioner concluded Tower Hamlets mayor Lutfur Rahman breached election rules and must vacate his post immediately.
Four voters alleged he used "corrupt and illegal practices" in last year's election, which must now be re-run.
Mr Rahman, who denied any wrong-doing, has been banned from standing again.
At the special High Court hearing, Election Commissioner Richard Mawrey also ordered Mr Rahman to pay £250,000 in costs.
One of Mr Rahman's aides, Alibor Choudhury, was also found guilty of corrupt and illegal practices.
Tower Hamlets First, Mr Rahman's party, said the judgement was a "shock" and it was seeking further legal advice in relation to a judicial review.
Mr Mawrey - who sat as a judge - said the mayor had "driven a coach and horses through election law and didn't care".
In the Election Court judgement, he said the effect of his ruling that Mr Rahman's election was void meant it was as if the election "had never taken place" and he had not lawfully been mayor since he was re-elected for a second term on 24 May 2014.
Mr Mawrey also added: "The evidence laid before this court...has disclosed an alarming state of affairs in Tower Hamlets.
"This is not the consequence of the racial and religious mix of the population, nor is it linked to any ascertainable pattern of social or other deprivation.
"It is the result of the ruthless ambition of one man."
Mr Mawrey also described Bangladesh-born Mr Rahman as an "evasive and discursive witness whose evidence was untruthful on occasion" and suggested he had played "race" and "religious" cards.
By Karl Mercer, Political Correspondent, BBC London News
Mr Rahman's career in politics looks like it is over, unless he successfully challenges today's ruling.
But the implications of the case could be felt much wider than a courtroom on The Strand. How will the Bengali community in Tower Hamlets, many of whom voted for Mr Rahman, react? What will the judgement's impact be on community cohesion?
And for the government - should the Law Commission be asked to look at making it easier to challenge elections if there is a suspicion of fraud?
It took four local individuals in this case to risk a legal bill of hundreds of thousands of pounds to get this election overturned.
The re-run poll is likely to be on either the 7 or 11 June.
Mr Rahman ran a "ruthless and dishonest campaign to convince the electorate his rival John Biggs was a racist", Mr Mawrey said.
After the ruling, Labour London Assembly member, Mr Biggs, said Mr Rahman and his allies had "robbed the people of Tower Hamlets of the free and fair mayoral election they deserved and betrayed everyone in our community who trusted and voted for him".
The group of voters who brought the action was headed by Andy Erlam, who stood as a councillor. He said it was "a fantastic result for democracy".
The four voters mounted the legal challenge under the 1983 Representation of the People Act.
Their lawyers made a series of allegations, including "personation" in postal voting and at polling stations and ballot paper tampering.
The Election Commissioner upheld a number of the allegations, including:
- Voting fraud: ballots were double-cast or cast from false addresses
- False statements made against Mr Rahman's rival Mr Biggs
- Bribery: large amounts of money were given to organisations who were "totally ineligible or who failed to meet the threshold for eligibility"
- Treating: providing free food and drink to encourage people to vote for Mr Rahman
- Spiritual influence: voters were told that it was their duty as Muslims to vote for Mr Rahman. Mr Mawrey cited a letter signed by 101 Imams in Bengali stating it was people's "religious duty" to vote.
Lawyers for Mr Rahman, who was re-elected for Tower Hamlets First last May, described the claims as "invention", "exaggeration" and "in some cases downright deliberately false allegations".
The Election Judgement said Mr Choudhury, who was also found guilty of illegal practices, must immediately vacate his seat as a councillor and a new by-election must be held in the Stepney ward.
In a statement, Tower Hamlets First said: "The Mayor strongly denies any wrongdoing and had full confidence in the justice system and so this result has been surprising to say the least."
Communities Secretary Eric Pickles said the Election Court's judgement justified his decision to send commissioners into the council last year to take over some operations.
He said: "This judgement vindicates our action to intervene."
He added the judgement against Mr Rahman could mean extra powers being handed to commissioners.
The Met Police said it takes allegations of electoral fraud and malpractice extremely seriously and would take time to consider the election judgement.
Speaking to BBC London 94.9, former London mayor, Ken Livingston, said he found the result of the Election Court "worrying".
He said: "Let's wait and see if he is convicted of anything. The decision of the voters to put Lutfur Rahman there shouldn't be overturned by an unelected bureaucrat unless he is arrested."