[WHSmithIV]

That spring should sit inside the trigger. Getting it back in there with the pressure on the bar isn't going to be easy. It goes in from the bottom side of the trigger then the bar gets pressed up until you get the holes for the trigger bar pin aligned. The only way I think you'll get that back together is using a small vice to compress the spring with the bar until the pin holes are aligned then tap the pin back in. A third hand may be needed to do that to gently put pressure on the trigger while the vice is screwed closed.