it depends on why you left and who you left
If you knew that your outfit was not likley to be around (eg XL) i woulnd't worry about it too much, likewise if you have been made redundant and owe a training debt (rather than a bond) i would offer to pay £10 per month, there isn't a court in the land that will enforce payment of £300+ p/month against some one who can't pay, ie out of work as a result of being made redundant by the same outfit seeking enforcement.