But now the leaders of 1,224 businesses have added their voices to the chorus – after the Institute of Directors asked its members how they feel about the referendum debate.
The top line? Business leaders are split 63-29 in favour of remain, with six in 10 saying access to the single market is important to them – but three-quarters insist the EU needs reform.
Here's what they think:
1. They rely on the EU more than we realise
Some 42 per cent of leaders said they export to services to Europe (while only 21 per cent said they export goods there) – but 39 per cent said they employ people from the EU. Just 17 per cent said they have no links with the continent whatsoever.
Continued access to the single market was vital for 58 per cent of those surveyed – although 20 per cent said it wasn't important.
2. They want reform
Although 37 per cent said they strongly agreed and 21 per cent said they tended to agree the benefits of the UK remaining a full member of the EU outweighs the negatives, an overwhelming number said the EU needs reform, with 74 per cent either strongly agreeing or tending to agree an unreformed European Union is on a path of economic decline. That's a strong message to the Treasury.
3. They think the UK could make a go of Brexit
While business owners said access to the single market was important, they were also pretty optimistic about the UK's prospects if it does vote to leave the European Union.
Some 28 per cent strongly agreed, and another 22 per cent tended to agree, that the UK could make an economic success of leaving the EU. So perhaps all those warnings about the impact on jobs and house prices and the manufacturing sector, etc etc, are being viewed with suspicion.
4. They're downright optimistic about Brexit's impact on red tape
Business leaders are pretty scathing about red tape at the best of times – but it's telling that 46 per cent said a Brexit will have a positive impact on social and employment legislation.
That said, they were less positive on the impact on skills, with just under half saying leaving the EU will have a negative impact on access to skilled migrants.
5. They want the Norway option
If the UK does vote to leave, the "Norway option" – the arrangement giving Norway and Iceland access to the single market but no ability to negotiate or vote on EU legislation – was favoured by 36 per cent of those surveyed.
That was followed by 31 per cent, who would rather the UK just maintains its relationship through the World Trade Organisation, rather than having a specific agreement with the EU.
6. They're worried about how Brexit will affect trade
The t-word was the major issue for most of those surveyed – 53 per cent said a Brexit will have a negative impact on trade, while another 38 per cent said it will hit the UK's ability to innovate.
Meanwhile, 49 per cent said if the pound were to "significantly" depreciate after a vote to leave the European Union, that would have either a slightly or a very negative impact – compared with the 28 per cent who said weaker sterling would be either slightly or very positive.