I stumbled upon this great website the other day that has some fascinating aerial photos from 1950's with several showing the tilley factory at Hendon. If you register for free you can see higher res images. The one on this link near the botom has a van that cleary says tilley lamp on it. Just search for 'Tilley' on their site to see the other images. http://www.britainfromabove.org.uk/image/eaw035144?search=Tilley&ref=15 Paul
I know the first factory's were in Stoke Newington and Shoreditch W1 and on adverts it says Brent works Brent street NW4 but this photo from above shows Colindale avenue which is Nw9 a borough of Barnet but has its main shopping precinct in the borough of Brent There must have been two Hendon factories this https://www.flickr.com/photos/memories_hendon/8641720763/ shows the Colindale avenue factory which must have been just before it closed judging by the cars in the photo. It looks different to the aerial photo of 1951 and the area must have changed quite a bit. Did the two factories operate at the same time. The colindale avenue address is Brent works and the Brent street address is also Brent works.
Colindale avenue is in Colindale near RAF Hendon museum and the same road as Colindale station. Brent street is in Hendon and probably only a mile or two away.