A former head of the UK’s anti-fraud agency has accused his predecessor of having a “special relationship” with a criminal lawyer who allegedly engineered a wrongful criminal investigation into mining company ENRC.

Sir David Green said when giving evidence in London’s High Court that he wanted to shut down the relationship between Richard Alderman, his predecessor as director of the Serious Fraud Office, and Neil Gerrard, whom ENRC is suing for negligence.

Green also said he had raised concerns when he took up the role in 2011 about secret meetings Alderman had conducted with companies under investigation and leaks allegedly from within the SFO to the press of confidential case information.

Green was giving evidence in ENRC’s £70m lawsuit against the SFO, Gerrard and his former law firm Dechert. ENRC is suing the SFO for misfeasance in public office for allegedly launching a wrongful criminal investigation into it despite having insufficient evidence.

The company is suing Gerrard, a lawyer it hired in 2010 to investigate a whistleblower’s corruption allegations, for allegedly using ENRC as a “cash cow” by concocting a plan with the SFO to expand the probe. The company alleges Gerrard wanted to generate millions of pounds in unnecessary legal fees and the agency wanted to win a high-profile case.

The company also accuses Gerrard of sharing damaging information about ENRC with Alderman, whom he was friendly with, in order to continue the investigation. Gerrard has denied that he breached his duties to ENRC. The SFO, which is still investigating ENRC, and Dechert also deny the claims against them.

Green said in court that when he became SFO director he had “gathered . . . that [Gerrard] had some kind of special relationship, something like that, with Alderman”. He said: “I got the impression . . . that [Gerrard] was somebody who perhaps I ought to make clear to that things had changed at the SFO.”

“I wanted to change that to make sure it was clearly understood among the London legal community that there was no special access, there weren’t any relationships like that and the SFO was there to investigate and prosecute,” he told the court.

In his written witness statement Green said he had also expressed concern to Alderman about “private discussions” the latter had had with individuals under investigation by the SFO

When asked by ENRC’s barrister, Nathan Pillow QC, whether it was “improper” for contacts between Alderman and corporates under investigation to not be recorded, Green said: “I would have regarded that contact as dangerous and I would not have acted like that . . . I would expect it to be recorded.”

Alderman is not due to give evidence in the trial.

ENRC accused the SFO earlier in the trial of keeping the ENRC investigation “off the books”.

Tuesday’s hearing comes after Gerrard told the trial on Thursday that he had suffered several bouts of amnesia, after texts presented to him in court forced him to change evidence he had given.

Gerrard admitted he had “failed in [his] duty” to pass on information that the company’s former head of compliance, Cary Depel, was to be interviewed by the SFO. The lawyer had previously said he had had no knowledge that the agency was interviewing Depel, however a series of newly disclosed text messages showed Depel had informed him of it.

Another barrister representing ENRC, Clare Montgomery, said in response that Gerrard’s amnesia appeared only to cover “any facts or matters that might assist ENRC’s case . . . ” and accused Gerrard of having “lied to the court”. Gerrard said he did not remember those messages.

The trial is expected to last until next month.