Have you thought of applying for his mother's Will (with Codicil)?
The surviving executors are named as her son Edward Scott Sanderson, Esquire, and John Tymbs, of Worcester, Gentleman.
I have no idea what it would cost, but you can apply for it on the probate search service UK website. (That link is to the page for her entry, so you don't need to hunt through the rest of the pages.)
Edited to correct "her" to "his mother's", because that was out of nowhere for this thread, even if it tracked in my brain.