Lego was a off really as he freely admits that the company is still going strong and it's far from ever being British.
I can't imagine making a house out of Stickle Bricks (originally from Denys Fisher).
Tonka would have made sense but Tonka would have lacked the building element.
Trumps and Fighting Fantasy Books could do with a bit of a rival and bedroom computer game programming but I doubt if James would get that.
It's hard to imagine that a whole generation grew up playing successful computer games that were written by slightly older kids in their bedroom.
That would be educational and almost anyone with a bit of training could do it.