“I am the head of Chemistry in a Scottish Secondary school. One of my senior pupils is investigating methods of determining copper and iron in 2p coins.”

http://www.whatdotheyknow.com/request/copper_content_in_a_2p_coin#incoming-20865

The answer supplied ten days later was 7% Copper and 93% mild steel (with tolerances also disclosed).

This is a really good simple example of the benefit to the public from Freedom of Information laws in general and WhatDoTheyKnow.com in particular.

I have incorporated the Royal Mint’s response into this Wikipedia article:

Two pence (British decimal coin)