Private.
A few weeks later I would tell my 3 siblings and a couple of people I consider friends that I had won a smaller but still life changing amount for us all.
1m to support me, a couple of dogs, a few ponies and several cats for the rest of our lives.
At least one property in every city and major town for use by WA/women's refuges.
A few centres around the UK to diagnose and support anyone with autistic conditions especially adults that are struggling with the NHS and can't afford to go private.
A foundation set up to support anyone that needs it à la Alison in At Home with the Braithwaites.
Then I would continue with my private, solitary, frugal, very stuck to home, animal obsessed life exactly as before. Except I would never have to speak to another person ever again unless absolutely necessary 
But if the Gods are listening I would actually be just as happy with about £300K, that would give me a very secure if less generous version of the above.