Information provided by whistleblowers provides grounds to suspect that the Vote Leave campaign broke electoral law during the 2016 EU referendum campaign, according to a legal opinion obtained by the men's lawyers.
And the opinion said there were "reasonable grounds" for the Electoral Commission to investigate the possibility of a conspiracy involving two senior members of the Leave campaign now working as advisers to Theresa May in 10 Downing Street.
The 50-page opinion obtained by Bindman's solicitors, acting on behalf of Christopher Wylie and Shahmir Sanni, called for an "urgent investigation" to establish whether a prosecution could be brought over allegations the campaign broke spending limits.
The allegations have all been denied by Vote Leave and its former officials, who reject all accusations of wrongdoing.
Witness statements and documents provided by the whistleblowers "strongly suggest" that a donation of almost £680,000 made by the campaign to a youth Brexit group called BeLeave was actually used for
the benefit of Vote Leave, to pay data firm Aggregate IQ for targeted messaging services, said the legal opinion, prepared by barristers from Matrix Chambers.
If this cash was recorded as Vote Leave expenditure, it would take the campaign's spending over the £7 million limit, establishing a "prima facie case" that electoral law has been breached.
There are "realistic prospects" that the group and official David Halsall might be convicted, said QCs Clare Montgomery and Helen Mountfield and barrister Ben Silverstone.
And they said there were "reasonable grounds" for the Electoral Commission to investigate whether any offences where committed "with the knowledge, assistance and agreement" of senior figures in Vote Leave, including Stephen Parkinson and Cleo Watson, who are now advisers to the Prime Minister, as well as the campaign director Dominic Cummings.
"Given the very close working relationships at all material times between Vote Leave and BeLeave, the way up which Mr Parkinson and Ms Watson supervised the work of the young BeLeave volunteers and that Vote Leave and BeLeave staff worked closely together on a daily basis, in the same office, throughout the referendum campaign, it can be properly inferred that Mr Parkinson and Mr Watson must have known about BeLeave's campaign activity, of which the AIQ targeted messaging was a significant part," said the opinion.
"In these circumstances, there are certainly reasonable grounds for the Commission to use its powers... to investigate whether any election offences committed by Vote Leave and Mr Halsall were committed with the knowledge, assistance and agreement of other senior figures/officers in Vote Leave, including Mr Parkinson and Ms Watson."