The 'remain' camp received an additional boost with the publication of a Confederation of British Industry poll yesterday, which showed that 80 per cent of nearly 800 business leaders want to stay in the EU, with five per cent in favour of leaving and the remainder undecided.
However, the CBI said it would not align itself with either the 'leave' or 'remain' campaigns.
Meanwhile, Leave.EU said it had been helping to organise "the biggest series of public meetings since the Second World War" alongside Grassroots Out.
Leave.EU spokesman Jack Montgomery added: "We'll be taking these to every corner of the United Kingdom and beyond, all the way to the Rock of Gibraltar, as the campaign enters its last 100 days, as well as launching massive, country-wide action days with hundreds of stalls and thousands of campaigners every weekend."
Rival Vote Leave said its campaign team had grown from eight people working in an "empty shell" to 60 full-time staff and volunteer-led campaigns across the country.
Head of media Robert Oxley told PRWeek: "After the PM’s deal failed to bring powers home in the renegotiation we have a once-in-a-lifetime opportunity to secure real change by Voting to Leave in a hundred days."
Public affairs professional Chris Calland, of Hanover Communications, said both camps had used the power of "unexpected voices" making the case to leave or remain during the campaign so far and he pointed to comment pieces by former Top Gear Host Jeremy Clarkson and General Sir Mike Jackson at the weekend as examples.
He added: "Voters increasingly tune out the usual comment from the usual subjects. Notice how 'leave' campaigners are reluctant to feature Nigel Farage. That’s why the appointment of German-born Labour MP Gisela Stuart to co-chair Vote Leave makes sense. She reaches the people who can’t be reached by her co-chair Michael Gove and vice versa.
"But most interesting were the articles in the Sunday papers by Jeremy Clarkson and former head of the Army General Sir Mike Jackson. Their interventions could be seen as 'eurosceptics for Europe' and were carried in eurosceptic papers. Their arguments were all the more persuasive for being unexpected in both substance and tone. Quite a coup for the 'remain' campaign."