According to the ILM's research, respondents gave a damning indictment of the leadership qualities of the three main UK candidates, indicating that it's not just Brown who has his work cut out to position himself as a credible and effective leader ahead of the Election.
The survey of over 2,000 managers assessed nine leaders from across the worlds of business and politics on the five fundamental aspects of leadership - ability, personal integrity, vision, communication, and engagement - and generated an overall leadership quotient (LQ) score for each.
And while Brown scored badly on the personality aspects, his integrity is seen as his strong point. By contrast, David Cameron's strong communication skills are offset by a perception that he lacks integrity. Nick Clegg performed most strongly on integrity, but his lower profile and political inexperience resulted in the lowest score on leadership ability.
Brown came bottom of the league with a leadership quotient of just 4.5, which was dragged down by low scores in the key areas of engagement (3.69) and communication (3.91). Cameron received the highest score of the three main UK party leaders at 5.66, while Clegg scored 5.20.
Richard Branson was perceived as the most capable leader, with a score of 8.06, followed by Barack Obama (7.76) and Angela Merkel (6.20). The three UK political party leaders also scored lower than other well-known business figures - the vice-chairman of West Ham United, Karren Brady (6.0), and controversial media mogul, Rupert Murdoch (5.83).
The research - Politics: Leadership Matters - reveals 26% of managers are undecided about which party to vote for, suggesting there is an opportunity for each candidate to address their perceived weaknesses as a leader to win these voters over in the run up to the election.
Almost one third (30.5%) of respondents voted Labour in the 2005 general election but only 16.4% intended to do so in 2010. While committed Labour voters gave Brown an LQ of 6.73, this plummeted to just 4.37 among those who had voted Labour in 2005 but would not do so in 2010.
Penny de Valk, chief executive of the ILM, said: "We wanted to unpick just how significant an individual leader's overall capability is to their party's chance of success. This clear swing of Labour voters to other parties on the grounds that they lack confidence in Gordon Brown's leadership skills shows that perceptions of the candidates' leadership qualities will play a pivotal role in the next general election.
"Traditionally, we expect policy and integrity to form the bedrock of political leadership, but what we see here is the importance of communications and engagement - the politics of personality. Gordon Brown is seen to have the substance, but does he have the required style?
"Barack Obama was shown as the outstanding political leader in this survey, and the 2008 US election saw a huge swing of voters gravitating towards his dynamic brand of leadership. By contrast, in the UK, Cameron and Clegg appear to be gaining support by default.
"With over a quarter of managers still deciding how to vote, there's still much to play for over the next few weeks; and public perceptions around their leadership qualities are going to be crucial."
How the leaders compare (leadership quotient).
1 Richard Branson - 8.06
2 Barack Obama - 7.76
=3 Karren Brady - 6.20
=3 Angela Merkel - 6.2
5 Rupert Murdoch - 5.83
6 David Cameron - 5.66
7 Nicolas Sarkozy - 5.44
8 Nick Clegg - 5.20
9 Gordon Brown - 4.50