i was told by the forestry commission that once the main stem has been eaten by deer, they wont grow very tall. the trunk will then have offshoots so will grow width ways rather than tall. alot of our trees are like this and are difficult to walk underneath without cutting back the lower branches.
in my understanding, if the tree was 5ft high when it was nibbled, then the main trunk wont grow above 5 ft. speak to the forestry commission, they are very helpful and will often come out to advise.
personally id buy some new stock and protect them with tubes and a stake.