Suddenly come into some money? Here are three ideas to invest a £500 lump sum. : If you suddenly find yourself £500 richer, it can be very tempting to go out and spend this money immediately. However, while £500 might not seem like very much in the grand scheme of things, using this money to give yourself a one-off treat might not be the best decision. According to the latest figures from the Office of National Statistics, UK household finances are in a worse state than at any time in history.