Looking at the UK Gov websites, it would appear that one has to have quite severe mental incapacity in order to be ineligible for jury service.

Autism/Apergers is on a sliding scale of disability, so a blanket exclusion would be unworkable.

I would agree with you Jack on principle that the seriousness of deciding a verdict in a Court of Law requires absolutely normal mental capacity.

My niece has mild Aspergers, and would be a rather strange addition to any jury. But I fear that she would be obliged to attend nonetheless.
Not ideal. And not fair on the defendant either!