UK has very limited choice of milk powder, I went there in April this year and the brands that's available (which are also available in HK) are Aptamil and Cow & Gate. I never see any Enfamil A+. It seems all the shops (including supermarket and drug store) sell the same brands. My son drinks Neslac but I can't find any there, I have to try both Aptamil and Cow & Gate, but he doesn't like them. He lost 2 pounds after his trip. It's best to bring your own milk powder.
There have only SMA (old brand name of S-26) , Cow & gate, Muilupa, Farley at Boots shop. You can check with the Boots website for more information. My son drink S-26 although SMA is similar I also brought my formular to UK. I never see Enfamail A+ in UK. Actually, UK babies will drink fresh milk after 1 years old, milk for their babies is free of charge & free delivery until 3 years old.