Arnell's Dagenham Symphony (1952) is actually from a film score about a Ford plant opening (
http://en.wikipedia.org/wiki/Ford_Dagenham). They cobbled together all the sections with Arnell's sanction.
The Sinfonia (1938) was written in London before he left for the US. His daughter gave it to Martin Yates when she came over for the funeral. Her mother (I think Arnell's first wife) had it stuffed in a box in Nebraska. So, it's a sizeable completely new work!
I should find out about the Matthews' 7th shortly (I hope).