The headteacher of one of the country's top private schools has accused the Daily Mail of setting an appalling example to young people as the paper faces a barrage of fresh criticism from leading figures in education, the church and media over its attack on the late father of Labour leader Ed Miliband.

Following the Mail's claim last week that Ralph Miliband, a respected leftwing academic who died in 1994, "had nothing but hatred" for British traditions and institutions "including our great schools", Anthony Seldon, master of Wellington College, told the Observer it was the Mail that was doing real damage to British education today.

"If the Mail speaks for Britain, it is not a Britain I want to be part of," he said. Referring to the paper's original article on Ralph Miliband eight days ago, which appeared under the headline "The man who hated Britain", he added: "It sets a very bad example to young people to belittle someone who is dead. I think it is nasty, it lacks taste and decency, and I worry about antisemitism.

"Everything that I value and try to get across to young people here, this seems to cut across. It is antithetical to everything I try to teach our pupils.

"The constant trashing of people for the sake of selling newspapers is demeaning and destructive of trust."

As investigations by this paper show that the Mail and Mail on Sunday are owned by a company controlled via an arcane network of financial vehicles based in two tax havens, the bishop of Bradford, the Right Rev Nick Baines, also attacks the Mail for damaging public life.

The bishop said: "It is not a matter of taste. It is a matter of the corruption of civic life and the public discourse to do what the Mail did with Miliband." It was disingenuous for the paper to defend itself by saying that headlines should not be read alone, but along with the entire text underneath. "The Mail knows exactly what it is doing. I believe it is both corrupt and dangerous," Baines said.

The comments by Seldon and Baines will fuel an increasingly charged debate over press regulation which will come to a head this week when senior MPs in the privy council meet to discuss how to respond to the inquiry into press standards by Lord Justice Leveson. The Mail's editor Paul Dacre, who is chairman of the Press Complaints Commission's editors' code of practice committee, is in the vanguard of efforts to ensure that the newspaper industry retains the overall right to regulate itself, against those who want more independent oversight.

The Labour leader, who was given the right of reply in the Mail on Tuesday, only for the paper to reprint its original piece alongside his reply, as well as a stinging editorial, has asked to speak to Dacre and Lord Rothermere, chairman of parent firm the Daily Mail and General Trust (DMGT), but neither has responded. "It is astonishing," said a Labour source, "that someone who claims to be defending the great British institutions refuses to pick up the phone to the leader of the opposition."

On Thursday the Mail on Sunday apologised unreservedly to Ed Miliband after one of its reporters intruded on a private memorial service, held on the 29th floor of Guy's hospital in London, for the Labour leader's late uncle. But the Daily Mail has not done so.

Lord Justice Leveson could himself be dragged in to the row this week. Lord Soley, a former chair of the parliamentary Labour party who sits on a committee investigating how judicial inquiries are run, will question the judge. He said: "The recent stories in the Mail and the Mail on Sunday show that some editors and journalists have learnt nothing from the crisis that led up to the inquiry.

"I shall want to know what Lord Justice Leveson makes of this continuing problem. How does somebody like Paul Dacre stay in his job when the Mail under his leadership has been such a serial offender? The culture and ethics of journalism at the Mail is still profoundly wrong."

Investigations by the Observer have revealed that all of the voting shares in the DMGT, the floated company that owns both the papers, have been acquired by a financial vehicle called Rothermere Continuation Limited. RCL, which operates for the benefit of Viscount Rothermere, DMGT chairman, recently bought the remaining 11% of voting shares in the trust that it did not already own. According to a declaration made to the stock exchange in August, RCL "is a holding company incorporated in Bermuda".

The declaration reveals that "RCL is owned by a trust which is held for the benefit of Viscount Rothermere (the chairman of the DMGT) and his immediate family. Both RCL and the trust are administered in Jersey, in the Channel Islands".

Both Bermuda and Jersey are tax havens which, as the Mail explained in a recent article, are a "scourge" which "costs Britain billions". While there is no suggestion of any impropriety, the complicated offshore ownership structure sits uncomfortably with the paper's reputation for being the voice of Middle England.

A spokesman for the Mail, which has defended its coverage and rejected any claims of antisemitism, declined to comment on whether DMGT, Rothermere or RCL enjoyed any advantages as a result of their links to tax havens.

By Saturday night an online petition set up by Tony Blair's former spin doctor Alastair Campbell asking Dacre to debate his paper's attack on Ralph Miliband in public had attracted almost 80,000 signatures.

Speaking on Friday night's Have I Got News for You on BBC1, Private Eye editor Ian Hislop tore into the Mail's depiction of Ralph Miliband. "This is the man that hated Britain on the evidence of one entry in a diary when he was 16 when he'd just arrived as a refugee in this country. It was the most pathetic piece."

Despite a strong populist speech at his party conference and the publicity from the continuing war of words with Mail group newspapers, Ed Miliband's latest polling figures do not suggest a bounce in popularity for his party.

As both parties prepare for imminent reshuffles, an Opinium/Observer poll has Labour on 36%, just 5 points ahead of the Conservatives on 31%. The Liberal Democrats are on 7%.