Thanks Gents.
The lady I spoke to this morning thinks the locking mechanism needs replacing.
I have been told to allow up to the standard 28 days for the repair to be completed.
It is still covered under the warrenty terms, as Canon allow for an extra month.
Its gone now so hopefully it won't be too long before it is back.
For future reference, here is the service centres address:
Canon UK RCC
P.O BOX 630
Borehamwood
WD6 9AW
Tel: 02087314134