Forget the scary stories; the UK is indeed a strong country and won't disappear if it leaves the EU. But will the average UK Jo be better off? I don't think so.
My main concerns are:
1. Employment laws; the UK has been working at EU level to weaken employment protection laws. Essentially that means, less rights for workers, more freedom for employers. Thankfully, it hasn't succeeded to do so, but if we were to leave than you can be certain of weakening in employment protection.
2. Immigration; that's a joke really, but an effective one. Having failed huge numbers of its own people by not educating them and helping them get out of benefits the UK economy is in need of immigrants for way too many professions (not least education, healthcare, engineering and technology). Leaving the EU will not change the slightest bit of this. Plus leaving the EU and maintaining a trade agreement with the EU will automatically mean maintaining open borders for EU citizens. Just see Norway and Switzerland for examples. Open borders for trade means open borders for people. Period. Unless anybody thinks they don't need EU trade?
3. Lack of democracy? I know, I know the EU sounds like a bunch of unelected bureaucrats which really sounds undemocratic and we hate it. But is this how things are? I had to go through a couple of books and a lot of news reading to understand how the EU works (I guess there must be an easier YouTube video somewhere?!), but most of EU's decision making power is with people who have been elected. That's not the EU Commissioners (they still have to be approved by the elected EU Parliament) who actually cannot make final decisions by themselves. Commissioners only propose legislation which then has to be agreed by groups of ministers - for example environment ministers of each EU country will discuss and decide on environment related policies.
4. Environmental / energy laws
The rest of the world is marching towards renewables. Germany regularly regularly covers 70% of its electricity needs by renewables without polluting. Not saying they are perfect (far from, for many reasons); just saying it is doable and that this is the direction we should be moving to. That is if you (like me) mind breathing polluting emissions and contributing to climate change. Which is the only developed country in the world that removes subsidies for renewables and makes a point out of reducing investment in renewable energy? UK I'm afraid. And similar with employment laws the UK has been lobbying to weaken environmental protection and energy cleaning laws at EU level (sometimes succeeding). Even recently (post VW-scandal) the UK led the opposition to stricter vehicle emissions laws at EU level.
5. Economy
So you can't believe all the world's economists that tell you the UK will be worse off if it were to leave the EU? No IMF? No Bank of England? No way? They must all be lying (unlike Boris)! Like I mentioned in the beginning the UK, won't disappear, it's not about that. But get ready for our pounds to worth significantly less (already feeling the heat). Get ready for more action because of trade tariffs...
6. Corruption Tory style.
I'm not a fanatic of any party but I have been observing politics in this country for almost 10 years. I have been looking even closer to areas I understand well (energy/environment/economy with that order!). A lot of what I see recently makes no sense at all unless they are trying to push for their friends interests for some quick £££. Those that really stand to gain from BREXIT are those who can much easier convince UK ministers than EU wide governance, for their dodgy deals. Local corruption is always easier than wider/broader one.
Finally, yes, the UK is an important country but don't forget that the UK (and every single EU country, including Germany, France etc) is on a fast track to becoming a less important country. Asia is growing on unprecedented rate, that's not just China, that's many more Asian countries. Countries which because of fast population and economic growth rate will sooner or later be very important global players. The UK can see them as yet one more declining empire or as a very strong part of a powerful union. I'd choose the second.
PS: don't get me wrong with all this; I undoubtedly want the EU to change from its current mess to a really powerful union. The potential is there, but it needs nations and leaders that can see the vision to a United States of Europe. I can't believe I just agreed with Clarkson here!