I believe there are a number of issues, some of which are highly controversial.
The population is aging, operations are now being carried out in people over 80 that a few years would never have been done as it was too risky. Most admissions to hospitals I understand are for the elderly. With the population predicted to have an ever older profile and will have more people retired than working it's likely to be a situation that no party can resolve.
There is a lack of doctors and nurses due to a reduction in places at teaching hospitals a number of years ago. This will take time to fix as it takes a number of years to train people. There are lots of beds, the wards didn't disappear just closed / moth balled!
The care needed for when a person can leave hospital is in short supply causing bed blocking. Relatives / family in general no longer feel any obligation to look after their family as they once did, preferring to live their lives and have the state provide. Care homes and care at home is expensive and with the prospect of people being charged higher levels is likely to push people into 'staying 'in hospital longer.
The culture of blame and litigate has created a lot necessary paperwork that didn't previously exist. It also depletes funds fighting spurious claims.
The cap on pay for civil servants has created an artificial market that isn't attractive for highly talented managers. It's very popular to blame 'fat cat' managers however, few people understand the complexities or could manage a £1+ billion budget and 20K staff. The size of a large trust. That's larger than most FTSE 100 companies, the directors of which earn a factor of at least 10 more than a typical NHS CEO. Most people don't seem concerned about what a foot ball player or pop star earns, but god help anyone earning more than £140K in the NHS. The result of this artificial market is that the best most talented people will naturally go for the appropriate reward....,the private sector. It's a global market for those who have talent. Foot ball players move to clubs around the world that pay the most, so do highly creative, value creating managers.
There is a lot of money about that could fix most of it. Overseas aid is massive, and it's a decision to increase it that was made a few years ago that was missed by most in the manifesto that included it. The proliferation of government to meet the aspiration of local accountability carries a high cost. The UK has four parliaments (London, Ireland, Wales, Scotland), and the introduction of local Mayer's is also being rolled out.