Start a 'cottage industry'.
If you're a dab hand at arts and crafts, try selling your jewellery and artwork, whether on eBay or at craft fairs. US websites Etsy and Redbubble are designed exclusively for buying and selling homemade goods. All prices are currently in dollars, but they offer live currency conversion. Some talented MoneySavers make big profits.
How much? Potentially £100s, depending on your spare time, artistic ability, and ability to sell yourself.