Claims that Remain campaigners breached spending rules have been rejected by the Electoral Commission.
Former international development secretary Priti Patel complained that three videos from lead Remain campaign group Britain Stronger in Europe (BSIE) should have been declared as “joint spending”.
Ms Patel, who resigned in disgrace after secret meetings with the Israeli government, also made allegations about late registration of campaigners associated with BSIE.
The Electoral Commission concluded there was no evidence there was joint working on the videos or grounds to suspect a breach of joint spending rules.
It said the company under investigation, DDB, also known as Adam and Eve, was a registered campaigner and reported spending correctly.
“In this matter, there is not sufficient grounds to suspect that BSIE breached the joint spending rules,” they said.
“It was alleged that five campaigners were set up by BSIE and acted under a common plan. The commission has not been provided with or found evidence for an investigation to be opened.”
A new investigation has been opened into another registered campaigner, Wake Up and Vote, over claims from Ms Patel that they incurred undeclared joint spending with DDB.
A previous commission investigation concluded extracts from two books published since the referendum, describing daily telephone meetings of certain Remain campaigners chaired by BSIE, did not meet the threshold for an investigation.
It said: “Evidence indicates the meetings were advisory and did not involve or result in decisions on referendum spending.”
A linked inquiry into allegations made by the BBC Northern Ireland programme Spotlight – Brexit, Dark Money And The DUP – is unable to proceed, said the commission.
The programme, aired on June 26 this year, made allegations about whether the DUP, currently propping up the minority Conservative Government, failed to declare joint spending with other EU referendum campaigners.
After requesting further evidence from BBC Northern Ireland, and being told that there was no “significant information” other than what was in the programme, the commission considered whether other evidence sources were available.
The commission concluded it “does not have grounds to open an investigation”.