One of the older gents at the allotment said to use tomato feed. Variety I had says high potash feed, also magnesuim and other trace elements which he said could also help.
2 chances in my book, his garlic seems very healthy. Another tip he gave me was to feed my tomatoes with epsom salts, one teaspoon to a gallon of water every other week. Normal tomato feed week between.
DD