The prominent businesswoman Amanda Staveley fell out with the former cabinet minister David Mellor as the pair worked on securing the billions of pounds that saved Barclays during the 2008 financial crisis, the high court has heard.

Staveley is suing Barclays for up to £1.5bn after her client, Sheikh Mansour bin Zayed Al Nahyan of Abu Dhabi, invested £3.25bn as part of an emergency fundraising 12 years ago. She claims that the UK bank was secretly offering superior terms to Barclays’ largest investor, the state of Qatar.

The financier alleges this concealment contributed to her firm, PCP Capital Partners, being forced off the deal as an investor and only being able to collect £30m in gross advisory fees. Lawyers representing Barclays have described the damages claim as “opportunistic and speculative”.

On the fourth day of the trial Staveley, who has just brokered the potential takeover of Premier League football club Newcastle United, said she had engaged a string of high profile advisers to work around the Barclays fundraising deal, including Mellor, Lord Digby Jones, Jonathan Aitken, the former politician, and Peter Middleton, the former chairman of Barclays.

Mellor had been looking for a fee of up to £5m, she added, but his payments were delayed after PCP was sidelined from the transaction.

“You will see how angry Mr Mellor got with me in his email. He was very, very stressed. That is why it was particularly sensitive,” Staveley told the court. “He was threatening to go to the press.”

Supporting legal documents filed by Barclays in the case said: “As one of the third parties who was due to receive some fees from the deal, Mr Mellor was very anxious about the delay in receiving payment and, after PCP lost its position [as a Barclays investor], he placed a great deal of pressure on me personally to resolve the situation by seeking reimbursement.”

The documents state that Mellor ended up being paid about £630,000 in fees.

Staveley’s witness statements also claimed that Roger Jenkins, Barclays’ then chairman of investment banking, had “lied” to her about the terms on which Qatar invested in the bank. She is accusing Barclays of concealing that it was offering her “manifestly worse terms”, as Qatar received £346m in fees plus an unsecured £2bn loan, despite Staveley’s claims that Jenkins had offered her the “same deal”.

Barclays has said that the fees had a commercial purpose and the loan was approved by its group credit committee.

The animosity between Staveley and Jenkins was further highlighted in written fillings to the court, which outlined how the Barclays executive told colleagues that his wife, Diana, deserved the credit for bringing Sheikh Mansour into the deal and not Staveley.

The document records an email sent by Jenkins to Rich Ricci, a former high-profile Barclays executive, which said: “[Staveley] gets all the limelight. And we know she was there to ex[e]cute what [Qatar’s Sheikh Hamad] teed up for us with Mansour. She had no clue.”

Staveley said Jenkins’ description was “incorrect”.

The case continues.