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I would be quite wary of this for another reason... You may be getting a better Click Thru Rate than you realise - thanks to the .co.uk - which you will lose if you switch to a .com

Perhaps try testing adwords with .co.uk versus .com and see if there is a difference.

These days many sites link (often site-wide) to their social profiles on Facebook, Twitter, YouTube.... etc

Theoretical SEO on-page optimisation might condone adding nofollow to these links, but I have a feeling it might not do much in terms of conserving page authority and indeed might be a bit of an "over-optimisation" signal.

Thoughts?