I EBF both for 6mo (first was pretty tough, second easy) then continued BF to when they were nearly 18mo. Was happy in principle to carry on feeding forever but they self weaned. they both seem like reasonably healthy kids but no better or worse than average. I guess we are lucky neither (touch wood) seem to have any long term health issues.
On the evidence - there is a recent lancet review and I think the most clearly proven health benefits for BF in developed countries (like the UK) are all, in term babies, infectious (chronic) conditions like:
*Upper respiratory tract infections (colds or more serious like bronchiolitis)
*Diarrhoea
*Otitis media (middle ear infection)
The "long term" health outcomes, like obesity, diabetes, don't seem as strongly proven. they show up in the observational studies (have not been proven in randomized trials like PROBIT) but in those, there is serious confounding to be considered. Babies that are born into less privileged homes are much more likely to develop obesity, in countries like the UK - this is the socioeconomic patterning of health outcomes (see Marmot, Danny Dorling etc) and it's very very hard to disentangle that from the effects of feeding. More affluent mothers tend to find getting BF established more straight forward, for reasons we don't fully understand. thus, the Lancet review concluded it wasn't clear that the association between feeding mode and diabetes, obesity was due to the BF. the other long term health outcomes - I don't think it concluded there was good evidence for links.
Therefore, the way I think about it is that the BF tends to help with these "chronic" infections of infancy that most babies tend to get at some point - making them less likely or less likely to be serious (needing GP appointment or worst case, hospital).
At population level, because these infections are so common - tens of thousands of hospitalisations for URTI/diarrhoea a year - and the effects of BF are quite good (maybe 30, 40, 50% reduction in the chance of them happenning), it's seen as a public health "win". At national level, a big impact on health service to have so many otherwise healthy little babies need to go to GP for antibiotics, go into hospital for rehydration or treatment, that well, if we can prevent this - why not? These are the major reasons that otherwise healthy babies need medical care - so why not try and prevent them?
At individual level, such problems are easily forgotten - 2 years later, do you remember the time your 6 month old had diarrhoea and you were worried so you went to the GP or to A and E? did it impact on long term health? Probably not. Easily treated and managed. Not something like, let's say a severe allergy, or epilepsy, or asthma, in needing constant management and specialist care throughout childhood.
So the national policy is well meaning and well placed in prioritising a "cheap", easy method of improving child health. Fair enough. But it doesn't take into account the difficulties involved for many mums in getting there, the intersection with work and day to day family life, etc - because it's all on the mum. No one else can BF for you!
Now, don't get me started on "support".... ha ha