Passage: The halfpenny coin's obverse featured the profile of Queen Elizabeth II; the reverse featured an image of St Edward's Crown. It was minted in bronze (like the 1p and 2p coins). It was the smallest decimal coin in both size and value. The size was in proportion to the 1p and 2p coins. It soon became Britain's least favourite coin. The Treasury had continued to argue that the halfpenny was important in the fight against inflation (preventing prices from being rounded up). The coin was demonetised and withdrawn from circulation in December 1984.

Question: Based on this passage, when did half pennies stop being legal tender?
Steam of consciousness below:

The important part for answering this question is: The coin was demonetised and withdrawn from circulation in December 1984.
So, the answer is December 1984.