One of Donald Trump’s former campaign managers, George Papadopoulos, who famously met Alexander Downer at a London bar in what some have said was a trigger for the Robert Mueller investigation into Trump-Russian collusion, says he feels vindicated after the release of a summary of the Mueller report.

The special counsel’s investigation concluded there was no evidence Trump and members of the president’s election campaign conspired or coordinated with the Russian government ahead of the election.

“The witch-hunt is over,” Papadopoulos said. “I plan on going on the offensive and hope the president does too. Declassification of surveillance material is paramount.”

Papadopoulos was one of Mueller’s first prosecutions. The 31-year-old from Chicago pleaded guilty last year and was sentenced to 14 days’ prison for lying to the FBI about his contact with Russian nationals and Maltese professor Joseph Mifsud.

Papadopoulos claims Australian, UK and US intelligence agencies targeted him and that Downer recorded their conversation at the Kensington Wine Rooms in May 2016 when the two met, along with another Australian official, Erika Thompson.

Downer, in an interview with The Australian newspaper last year, claimed Papadopoulos had told him Russia might use “damaging” material they had on Trump presidential rival Hillary Clinton in the lead-up to the election.

Downer said he passed the information back to Canberra “the following day or a day or two”.

The Wall Street Journal, quoting a diplomatic source, reported Downer passed Papadopoulos’s Russia information directly to the US ­embassy in London.

Papadopoulos’s book, Deep State Target, will be released on Tuesday and details his account of dealings with Downer, Thompson, Trump and others.

Papadopoulos denies he told Downer about Russia potentially using material against Clinton, although he said Mifsud told him weeks before the London drinks that Russians had “dirt” on Clinton.

In September last year Trump wrote on Twitter “key allies” had asked him not to release classified FBI documents related to the probe into Russian influence.

Papadopoulos believes the allies were Australia and the UK and he wants their involvement to be made public.

“While the (Mueller) report is likely mired in classified material, and most will likely never be revealed to the public, I do hope what is public is what Alexander Downer’s and Erika Thompson’s roles were and why Downer has become so protected,” Papadopoulos said.

Downer, Thompson and the Department of Foreign Affairs and Trade was contacted for comment on Papadopoulos’s claims.

Downer has previously shrugged off Papadopoulos’s spying accusation, telling BBC radio last year: “I’m not going to get into these sort of allegations.”