It’s the “Good Condition Bonus” you get back from Motability at the end of the lease period (assuming you haven’t smashed up the car!!. It used to be £250 but was increased as follows,
3yr lease – £600 GCB
4yr lease – £700 GCB
5yr Lease – £900 GCB
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!