[Yelwis]

    Error for "com.uk".

    This domain cannot be registered because it contravenes the Nominet UK
    naming rules.  The reason is:
      third-level domains may not be identical to a top-level domain.

    WHOIS lookup made at 00:32:52 13-Apr-2015

But edu.uk is available for the owner of edu.co.uk.

Other 2-3 letter domains seem to have been squatted (I tried several ISO codes and some newer generic TLDs).