Our HV also suggested 600ml per day, and that can include milk in cereal, yogurts, cheeses etc.
My DS has also never been much of a milk drinker, and usually only takes about 5oz in the morning, has 4oz with his cereal, has yogurts, cheese, some times custard during the day and a 9oz bottle in the evening.
Our HV also said that you cannot force them to drink their milk, and that if they are not taking as much as they should, then to start using it in Mash Potatos, custards, yogurts etc.
HTH
Paula x