Finally got a chance to play on my own track in the sun at the weekend. Gave me chance to see how the FT looked scale wise it's not in the correct wagon yet needs to be a French Pechot flat not an English D class but the sizes are very similar .
Thanks Monica it's 1:19 scale. A complicated scale derived from the 'O' gauge which had track 32mm apart which equates to 2 feet in real life. The narrow gauge railways that supplied the front lines in ww1 were all 2 foot gauge and a lot of industrial railways around the world still are. Hope all this makes sense it took me months to get my head round it. 16mm to the foot the English mixing imperial and metric "(shakes his head)"