There are indeed 2 distinct unpaid indexes for Ask.com (Global) and Ask.co.uk (UK). Similarly, Paid Inclusion is separated into 2 distinct indexes.
Ask.co.uk uses the global unpaid index by default and allows user to restrict their searches to the UK index by indicating this preference using a radio button. In both cases the urls from the UK Paid Inclusion index are searched
Submission through the Ask.com site will only get a doc included in the Global index. Submission through the Ask.co.uk site will only get a doc included in the UK index.