This is a good question. If you’re in the market for string you can buy it in many places. DIY store B&Q has 60 metres of cotton twine for sale. Their natural garden twine comes in at 50 metres. Mosey on down to supermarket chain Sainsbury’s and you’ll get general purpose string, although somewhat shorter at 40 metres. Other products and stores are available of course. “Caveat emptor” if your string comes up short.