More than a dozen people are drawing up legal action against Labour, after they were named in an incendiary leaked report that threatens to plunge the party into financial peril.

Claims covering the Data Protection Act, invasion of privacy and libel are all being considered and could be submitted to the party as soon as this week. The party, individuals and some media commentators are all said to be the subject of legal complaints as a result of the document’s release and remarks made about its contents.

The row caused by the 860-page document has been a huge blow to Keir Starmer’s hopes of uniting Labour under his leadership following years of infighting. It claimed that factional hostility towards Jeremy Corbyn contributed to the party’s ineffective handling of antisemitism complaints and undermined its 2017 election campaign. It also included criticisms of the party and some of its leading figures by staff members in private messages.

Since it emerged last weekend, some of those mentioned in the document have contacted lawyers, with each person said to be considering several different claims. It exposes Labour to a potentially huge bill should it lose in court or opt to settle.

The Labour party had made serious allegations about our behaviour. Many of us are now subjected to horrendous online abuse Potential claimant

John McDonnell, Labour’s former shadow chancellor, has said the report was commissioned by general secretary Jennie Formby and put together by the party’s governance and legal unit. It was due to be submitted to the Equalities and Human Rights Commission investigation into antisemitism in the party, but that move was blocked by Labour’s lawyers.

Mark Lewis, a lawyer who has been contacted by those seeking legal action, told the Observer: “There are lots and lots of claims. There are claims under the Data Protection Act, there are claims for breach of confidence or invasion of privacy and there are claims for libel. It is a very lengthy report that mentions a lot of people. I’ve been contacted by 15 people. Each one of them could well have several claims. What is going on is phenomenal. It’s a bit like the soldiers leaving a barracks that they have to desert and setting it on fire.

“For four years, people in Labour have said there is no antisemitism in the party, it’s just a smear. Now they say that of course there was antisemitism, ‘but it just wasn’t us’. They have not noticed the absurdity of their change of position. There are actions against the party, actions against individuals, actions against commentators. People need to be careful about statements that have been made. If this bankrupts the Labour party or individuals, so be it. Actions have consequences.”

One of those considering legal action, who asked not to be named, said: “Several of us are already in detailed conversations with a number of legal teams. The Labour party had made serious allegations about our behaviour. These allegations were never put to us and not a single one of us did anything other than to work towards the best possible result in the 2017 election. Many of us are now being subjected to horrendous online abuse directly as a consequence.”

Formby has told party staff that the inquiry into the report, ordered by Starmer and deputy leader Angela Rayner, will examine how it was commissioned, the culture it reveals and who leaked it. Local party branches have been ordered not to share it.