Lidl have 5m cable loops (8 or 10 mm diameter, couldn't be sure) for £7.99, £10 for a padlock and the loop. Not much use for leaving a bike for a long time, but might be useful for tethering a trailer or making sure the wheels on your trike don't go walkies if you're in the shops for a short while.
(And for the discerning survivalist looking to equip on a restricted budget there are 1 kg hand axes for £7.99..)
