European Union
The CBI has called for changes to the European Union Getty

Here we go again. Yet another trade association cum networking posse has come out guns blazing warning a Brexit from the European Union will be such a disaster that we will lose control over regulatory decisions, access to trade agreements and talent and – this is the cracker – that global corporations won't want to make their HQ in the UK.

The brains behind the latest warning is Tech London Advocates, a group that describes itself modestly as an "unrivalled collection of tech leaders, experts and investors uniting to form the most influential independent private sector group in London".

In research published this week, Tech London claims a huge majority – 86% of the people surveyed – want the UK to stay in the EU. Dig a little deeper below the headlines, though, and you will see the survey sample was of 300 members out of 2,000. Be that as it may.

The numbers were robust enough for Russ Shaw, founder of Tech London, to go on to claim the "overwhelming response [of the survey] has given us a clear mandate to call for a Yes response on behalf of tech professionals in the digital capital of Europe". So Tech London is launching its own TLA EU-Yes working group to campaign for staying in the EU.

That's all well and good, you might argue; any business or trade body has the right to spend its own money lobbying for what it sees as just for its members and its industry. Far better, too, for businesses to be transparent about what they want than skulk in Westminster corridors.

But even for a lobbyist, Shaw went overboard with his next statement on a possible Brexit: "Worst of all, it would send a desultory message to the global digital community –Britain is no longer open for business."

Really? Not open for business? Perhaps he meant the UK would learn from the US and put up protectionist barriers? Or does the American Shaw really believe Britain's long history of trading with, give or take, every nation in the world over hundreds of years is going to be wiped out because we might decide to renegotiate our trade agreements with the EU?

It is not by accident that every American bank of any note has its biggest operations in the City of London rather than in Paris or Frankfurt despite the best attempts of those cities to steal the City's business. Nor is it by serendipity that many big US companies such as Microsoft and Apple have opened offices in Cambridge; they are doing so because that's where the brains are ticking.

What is most staggering at this early stage in the debate over the outcome of UK's membership of the EU is that business groups such as Tech London can make these extraordinary statements with such certainty. You would think they would have learned to be more cautious in their assertions following the allegations that the CBI, the UK's biggest business lobbying group, used "dodgy" and rigged polling data in a survey two years ago showing eight out of 10 of its members are fans of staying in the EU.

Clearly the Vote Leave accusations, and its decision to challenge the CBI by referring its poll findings to the British Polling Council, has found a soft target. For Paul Drechsler, the new CBI president, was forced to admit at the annual conference on 9 November that there is no "one uniform view" on the EU among its members although, on balance, the benefits of being in far outweigh the negatives.

Like it or not, this is a humiliating moment for the CBI that represents some of Britain's biggest businesses and millions of workers. But if the CBI bosses are to win over the hearts and minds of those they represent – and the public – they will have to do better than scare them.

If the CBI does believe that, on balance, staying in the single market is of greater benefit for our future prosperity then it needs to provide sound facts, not outlandish scaremongering such as estimates made a few years ago that three million people will lose their jobs or that an exit will cost £3,000 per household.

People are not dumb; they know these claims are being made out of self-interest and are as inaccurate as someone blindfolded trying to stick pins on to the proverbial donkey's tail.

The same goes for all businesses campaigners – whether it is those in the pro-camp such as Sir Stuart Rose's Business Stronger in Europe, The CityUK, US banks such as Morgan Stanley and Bank of America who have also been shooting off arguing against an exit or the more sceptical Business for Britain lobbyists that have been just as wild in some of their claims.

There's an even more crucial reason for campaigners to argue their case with fewer clichéd warnings but more nuanced restraint. David Cameron is this week sending his list of reforms to the president of the EU, Donald Tusk. Why would you give your sparring partner the chance to throw you over the horns before you've even started the war dance? Not smart business.

Margareta Pagano is a business journalist who writes for the Independent and the Financial News. Follow her on Twitter @maggiepagano.