What are 'bronze' coins made from? Why are some magnetic and some not?

Traditionally bronze coins were made from an alloy of copper, tin and zinc. Since September 1992, however, 1p and 2p coins have been made from copper-plated steel. The change was made because of the increasing price in world markets of base and non-ferrous metals. The copper-plated coins are the same colour, weight, diameter and design as those struck in bronze and circulate alongside them. There is one notable difference. Copper-plated coins are attracted to magnets because of the iron content of the steel core, whereas bronze coins are not magnetic.

In 1998, 2p coins were struck in both copper-plated steel and bronze. We may decide to do this again because, by having this flexibility to produce in either material, The Royal Mint can better meet customer needs promptly and cost effectively.