To answer your other question, DD did not have autism but she did have a language disorder, dyslexia and dyspraxia, before she developed epilepsy at 12.
After the first tonic clonic and EEG, and the diagnosis was made - they did refer her for a MRI scan. The MRI scans at our local hospital did not apparently show anything abnormal, however she had a MRI scan at GOSH when 16 (they had a 3T MRI scanner, one of the best in the country at the time), which did show a congenital malformation in the brain - which caused the learning difficulties and epilepsy. They said it had been there all along on the earlier MRI scans. It's called a focal cortical dysplasia.
I see the Epilepsy Foundation does refer to them in that article, as being a possible cause for epilepsy and autism.
GOSH firmly believe that all children with epilepsy should be assessed for brain surgery (to cure the epilepsy) - the first step would be a MRI scan. If I were you, I would press for a MRI scan of DS. If he couldn't keep still or tolerate the noise, they use sedation on children with SEN if necessary.
Given his age, he is in transition between paediatrics and adult services, The Epilepsy Society has probably what is one of the top diagnostic centres at its HQ at Chalfont St Peters, run jointly with the National Neurology and Neurosurgery Hospital (aka Queen Sq). They also had a 3T MRI scanner - there might be a new generation of them by now, as DD last had one there in 2012.