Okay. I think some of the long-term risks are likely to affect the whole of the UK, really, and the fiscal position right throughout the UK. Not all the risks are unambiguously to the downside. So, just following on from what I was just saying about productivity, I think we're now taking a realistic central forecast of productivity growth, a bit lower than we had before. But, around that, I think there are risks on either side. So, we've taken a view, for example, on something that may turn out to be extremely material over the next five, 10 years and beyond, which is the impact of artificial intelligence—enormous breakthroughs there in the last few years, difficult yet to be sure what that might do to productivity. Some people are very optimistic about that, and, if they turn out to be right, and I hope they are, then we'd be upgrading our forecast on GDP growth in the UK, and that would roll out right across the UK; it would have as much impact on Wales as in other places. It would be very good for revenue and the fiscal situation, including the devolved taxes that come through for Wales. So, there's one risk that I think is symmetric, but could turn out to be too pessimistic now, or too optimistic, on productivity growth.
I think some other risks are perhaps more clearly somewhat on the downside, and some of them are near-ish term risks. Perhaps Tom will pick up the story on welfare spending and whether or not the rate of growth of sickness and disability benefits will continue to be growing as fast as it has been, or whether it will level off. I think our forecast now, it is that growth levels off. That may turn out to be too pessimistic, and I'm sure Tom will talk about pressures on local authorities' spending, which then affects the fiscal position for central Government as well.
I think two other risks—. One is what needs to happen to other elements of Government spending in order to comply with its target of increasing defence spending to 3.5 per cent of GDP. The story in the last 50, 60 years since the end of the second world war is that defence spending on average could come down a lot, and that made room for other types of spending that have grown a lot—health, education spending. Clearly, that's different now, and quite how you make room for a target to increase defence spending to 3.5 per cent of GDP—. It will, undoubtedly, cause issues.
Just finally, one of the difficult things to project for the UK that has a very big impact is what happens to demographics. Will the fertility rate stay as low as it has become in the UK, right across the UK, something like a fertility rate of 1.4, well beneath the 2.1 number that has a neutral impact on the population of the UK? To what extent will it be offset by something that is more of a policy choice for the Government, which is the levels of net immigration, which, so far, over recent years has more than offset the relatively low rate of births of children on average to women over their life, and has seen the UK population rise quite strongly?