As part of its review into political predictions, the PRCA polled 112 individuals - the majority of whom work in public affairs - for their forecast of the result. The survey was carried out over the four weeks to 25 May.
All but four respondents said they expected the Conservatives to form the next Government - with three suggesting there would be a coalition, and one individual make the bold prediction of a Lib Dem regime.
Asked for more detail, 49 per cent of respondents said the Conservative majority would be more than 50 but fewer than 100 seats. A further 36 per cent predicted a majority of more than 100, whereas 12 per cent felt it would be lower than 50.
A YouGov poll of the general public today predicts a hung parliament.
In other predictions in the PRCA survey, 87 per cent think the Liberal Democrats will make gains across the UK and 83 per cent believe the Conservatives will make gains in Scotland at the expense of the SNP.
Labour losses are expected in Wales by three quarters of respondents. Seven respondents went against the grain and predicted UKIP gains, but the majority thought there would be no representation in Parliament for Paul Nuttall's party.
Ex-Labour MP and now managing partner at Connect Communications, Andy Sawford, who is leading the PRCA project, said: "What is different about this election, compared to in 2015, and subsequently the EU referendum, is how divergent the opinion polls are, with the latest ones pointing to everything from Tory losses and a hung parliament, to a Tory landslide.
"This explains why only half of our respondents expect the opinion polls to be accurate within the margin of error."