Me and DH have discussed this in the past. DH felt he never reached his full height potential and we hypothesised the reasons why. In his case it was a home environment where the food was of poor quality e.g. low fat/diet cooking sauces used all the time, little fruit or veg, rice crispies for breakfast, tiny cheese sandwich for lunch etc. Even as a teenager there was only ever allowed the odd babybel as a snack. He used to be starving at school and by year 11 was buying packets of cookies and pringles from the shop for lunch. Consequently he must have been quite malnourished.
This is obviously pure anecdote, but on a population level these kind of behaviours must have an effect, particularly the low quality UHPF foods.
I also wonder if the UK has a comparatively higher burden of treatable childhood disease compared to the rest of Europe. The inability to get a GP appointment and the refusal to adequately treat infections (e.g. timely and accurate prescription of antibiotics) must have an effect. Children go for longer with untreated ear infections, tonsillitis, chest infections etc. If your body spends more energy fighting off infection, then it has less time for growth. Other European nations have better healthcare than us...and it shows. The Euro health consumer index 2018 ranked Switzerland, Netherlands, Norway, Denmark and Belgium as the top 5. The UK was down in 16th place, between Estonia and Slovakia.
As another anecdote, I had a horrific bout of bacterial tonsillitis at age 10 (middle of growth spurt). The GP refused to treat it with antibiotics for over a week, until I was going downhill quite quick. Was off school for 3 years in total. My DM attributes this to me never reaching my "future height prediction" which was calculated when I was a toddler (by about 2 inches).