This is a large tube as can be seen from the ruler and it is soft so I’m sure it is useable. 
 
Having said that it is a rare tube and comes with a box also supplied by the makers of the paint. 
 
The maker is Mander Brothers of Wolverhampton and they made good paint. 
I have used some of these in my work as a museum’s conservator and in my own artwork. 
 
The real benefit of using these old paints is that they have truly stood the test of time.