seems you have to contact them first and find out when the next one is
Can I visit the Triumph factory?
At certain times of year we offer a very limited number of factory tours of our Factory Two facility in Hinckley. These must be booked in advance. Prior to their availability, all dates will be advertised on this website and are available on a first-come, first-served basis.
Unfortunately we are unable to offer factory tours for large groups or on dates other than those advertised. Please do not turn up unannounced at our factories as there are no public facilities and entry will not be granted.
or the other option is go to the crisp factory like Al said..and see Lineker