A rare 1p coin from the 1880s featuring a unique ‘H’ mark beneath the date could fetch a hefty sum of £280. This tiny detail, visible only under a microscope, makes the coin highly valuable. Other pre-decimal coins also have potential worth, depending on their date and condition. Keep an eye out for low mintage coins, as their rarity increases their value. So, rummage through your spare change and check if you have any hidden treasures.