> (1) イギリス人**に**軽{かろ}んじられた。  
> (2) イギリス人**から**軽んじられた。

Both appear to be grammatically correct 受{う}け身形{みけい} and also have the same meaning:  
*"I was looked-down upon by English people."*  

> (3) 虎**に**食べられた。  

Appears to be grammatically correct 受け身形 and mean:  
*"I was eaten by a tiger."*  

So, if I can swapped "に" for "から" in #1 and #2, can I do the same with #3 and say:  
> (4) 虎{とら}**から**食{た}べられた。  

 #4 does not sound possible to me *(but maybe it is?)*.  
So, might it be that "に" is the standard/natural thing to use in 受け身形?  
Sometimes, "から" can be swapped in for "に", but in reality you'd need a native ear to sense when that is appropriate?