Does the '.com' TLD have priority over ccTLD variants when it comes to SERPs?

A few weeks ago, I purchased 2 duplicate Domains but with the following TLD Extensions:

www.domain.com
www.domain.co.uk

When I enter www.domain.co.uk, into www.google.co.uk, it appears as expected. Similarly, www.domain.com also appears.

That being said, www.domain.co.uk does not appear when I enter domain as a search query into www.google.co.uk. Instead, www.domain.com appears.

My first assumption was that www.google.co.uk was prioritising www.domain.com over www.domain.co.uk as both pages have duplicate content. That being said, why is the .com variant appearing over '.co.uk', even when the following criteria have been met:

• Google (UK): As you can see, I am performing the search on the UK variant of the Google Search Engine;
• User Location: I am performing the search from within the UK. My IP address is located within the UK;
• Hosting: Both Domains are hosted within the UK with no Content Delivery Networks in use;
• Webmaster Tools: .co.uk automatically targets UK audiences whilst I have set the .com variant as 'Unlisted'. This being selected with the view of .com targeting all other traffic outside of the UK;
• WordPress: Whilst there is a Maintenace Page up at present, both have native WordPress installations. .co.uk having en-gb with .com having the en-us installation;
• Canonicalisation: I have not implemented any Canonicalisation yet. The reason being is that I wanted to see how much of an influence Webmaster Tools > International Search would have on both websites;
• Links: With both domains not containing any notable content, there are no External Links. Furthermore, no Backlinks have been accrued yet. I understand that these would play a factor but for now, both domains should not have any 'benefits' from links.

Admittedly, both domains are missing content that would add to the Geographical signals but I would argue that they are currently 'like for like' at present. As such, being able to be fairly compared.

With the above in mind, why is Google ranking the .com variant over the .co.uk variant when it comes to a search query?

At present, I can only conclude that Google adopts the following attitude:

Google will prioritise '.com' TLDs, for search queries, unless the search query contains some location indicator.

Alternatively, maybe Google adopts something more akin to:

Google will prioritise '.com' TLDs, for search queries, unless both the search query and the domain's content suggests otherwise in terms of location.

Is anyone able to suggest why this is happening and/or whether my conclusion has any merit?