Over time, new coin types have been issued, leading to new coin families. In the UK, the new coin families are the white heptagon (the copper-nickel 20 pence and 50 pence), the round pound (round and yellow), the 2 pound coin (round and bicolour), and the new pound (issued since 2017: bicolour and 12-sided).
Of the UK families, the bronze coins have a smooth edge, as do the heptagonal coins, while round white coins (5p, 10p) are milled.