For a year improving NHS food was part of my job. Loyd Grossman had given up, Jamie Oliver had given up and was concentrating on schools, so how difficult could it be? 
I spent most of my time gibbering 'but WHY??', for example the majority of hospitals don't have their own kitchens - the meals are brought in ready-made and heated up, so if they don't have enough low-fat/halal/whatever diets in the building, tough, you'll have to wait for tomorrow.
And all the PFI hospitals where they have to pay a premium of about 1/3 for delivery. Why? Because the route to the delivery bays is too low or narrow and the standard food delivery lorries can't get in, so the hospital has to pay for the boxes to be transferred into two small trucks and two drivers...
And the majority of hospital patients being conservative over-60s who refuse to eat anything exotic like curry and demand classic meat+2-veg, which as we all remember from school dinners, doesn't cope with reheating well.
Apparently all the meals have to and do meet strict nutritional standards, but it's the getting the right meal to the right patient at the right time which is a nightmare - and a simple lack of staff who actually nurse, now that nurses aren't the ones with the responsibility of feeding and cleaning patients. I think the people who do that stuff now are called 'healthcare assistants' but they don't have much training and there's not enough of them.
There's some good hospitals out there, usually where someone dedicated has taken over food procurement, but almost always where they have their own kitchens. I spent 3 days in St George's a while back and the food was certainly respectable, if a little potato-heavy. Luckily I had an interpreter with me as otherwise I'd never have found out it was there, or got any, seeing as I was tied to the bed for the first day, and you had to walk down the corridor for it.