At last! I made a call to the head of Therapy Services, who was really efficient and took up our case (hopelss orthotics service failing to provide shoes), and a process which they said would take until Nov has miraculously resulted in a pair of sandals and boots which we picked up yesterday.
Thank you, everyone who helped with advice and support.
He's REALLY proud of his sandals. It's the first time in his life he has ever had more than one pair of shoes at the same time. He keeps saying 'I'll just put my boots on now' and then 10 mins later 'It's time to wear my sandals now'