This is the lady you need to contact for a key.
http://www.helenhowes-sewingmachines.co.uk/locks.html In the meantime, use a small flat screwdriver.
Also, if you get in touch with Helen, splash out an extra £1.50 and get yourself a hold-down. It looks as though yours is missing.
Now I need to stop gazing at your gorgeous machine and go to bed.... Good night!