Did any of the 'Big Four'ever build new locomotives for their rivals?

I recently read that at the LMS once considered ordering a batch of GWR Castle class locomotives from Swindon but the request was declined. I know that independent works like Vulcan built a lot of locos for the big four too, but did any of them ever buy new locos from a rival's works?

 

Stanier 8F 2-8-0s were built by the LNER, GWR, and Southern Railway, and eventually ended up with the LMS and/or BR Midland Region.

 

Were they not technically ordered by the Railways Operating Division rather than specifically for one company ?, i doubt a Swindon built 8F was ever constructed with the intention of ending up on the Midland region, though that's what happened in the event.

 

The request to the GWR by the LMS to build Castles on its behalf is very dubious Firstly the independent British locomotive manufacturers had obtained an injunction to prevent any main line company building engines for another main line railway. This followed the time when the LNWR had built engines for the L&Y, both LMS constituent companies, at a time when the L&Y had major workshop problems. The LMS were unlikely to try it again. Secondly, the Castles, like most GWR engines were outside the standard LMS loading gauge, particularly across the cylinders, and their route availability would have been greatly restricted unless very major modifications were incorporated, and it is difficult to see why the GWR should do this.

The possibility of borrowing the drawings to base a new design on the Castle is more likely, but exactly how much of the Castle design would have been reused is debatable. As already pointed out, the LMS eventually borrowed Lord Nelson drawings, although very little of that design was actually reused. It is significant that the eventual Royal Scots were three cylinder engines; both the Castles and Lord Nelsons had four.