How can I locate a suitable Residential School in the UK for an Autistic Child?

I am an education consultant here in the UK and have very long established overseas clients with a UK home in London which they visit regularly. Their ten-year-old son has been diagnosed with Underlying Autism Spectrum Disorder 299.00 (F84) and Attention Deficit/Hyperactivity Disorder (ADHD): combined presentation 314.01 (F90.2).

.They are seeking a residential school for him in the UK, ideally near London. He has good English as he has always been educated at a main stream English-speaking International School. Can anyone please steer me in the right direction as the majority of UK schools I have seen online appear to be Day Schools without boarding facilities. Anything you can recommend as a starting point would be very much appreciated.