Here are what I see as the big risks of brexit, in no particular order:
1. Lower immigration leads to an increasingly top-heavy population in that we have fewer young workers to support old non-workers. Young people’s pay has been declining for the last decade, which presents an additional squeeze, while rents are extremely high. We are increasingly expecting young people to subsidise growing amounts of necessary state spending, while ignoring the fact that younger people are making less money and have higher expenses. This is clearly unsustainable and reducing immigration unnecessarily hastens the problem, thereby giving us less time and opportunity to fix it.
2. Foreign investment stagnates. As the UK leaves the single market it will become less important for international corporations. Those with bases here will probably maintain those bases, but treat them as legacy operations while growing new EU bases. The EU bases will become more obvious targets for investment and the UK less, leading to a stagnation effect where the UK continues for a while on inertia which eventually tapers off.
3. Whilst the economy has performed reasonably well up until this point, it’s been based on an increasing reliance upon consumer borrowing since the referendum. I’m not going to argue that borrowing is an inherently bad thing (although in the case of consumers I might), but it shows a widespread lack of judgement that consumer borrowing should increase when known economic turbulence is ahead. Those debts are significantly less safe than they would be in a non-brexit world and should the economy slow down, it will hit the average person harder the more debt they have. And we all know how it looks when large amounts of debt suddenly become revealed as unsafe.
4. UK public spending is already in a state of high deficit. We’ve weathered this fine so far because we’re a strong and stable economy with sustained growth, and therefore we are a good and safe candidate to lend to. Brexit is likely to reduce our prospects and therefore our credit rating, making borrowing more expensive, leading to us having to enact austerity while we try to rebalance our economy.
BONUS UPDATE: 5. Not that I have any evidence for this, but it seems to me that well educated natives are increasingly not entering relationships and having children. We offset this a bit by immigration in that immigrants tend not to have succumbed to this to the same extent, and they see the value of aiming for achievement in their general life. The risk I see is that in 30 years we will have a generation of teenagers who are overwhelmingly from parents who are from poor backgrounds and don’t aim for anything better, i.e. they set up their children to fail.