Regarding which skit in the Joel Grey episode is the "UK skit" both answers (Pachalafaka vs Sherlock Holmes) are in a sense "correct".
When the show was being made, Henson no doubt had Pachalafaka in mind as the UK skit given its nature and traditional placement in the show.
But when the Joel Grey episode originally aired in the US, it contained Pachalafaka and omitted Sherlock Holmes. (This is why Sherlock is referenced as the UK skit in MC's episode guide). Note this was the case in the original US broadcast...it's quite possible that other countries that didn't air the UK sketches in the show's original '70's broadcast cut the shows differently...
...In fact in the original broadcasts, Canada and USA did choose different material to cut out. I lived in Ohio at the time (right on the lakeshore) so i was able to watch both the USA and the Canadian broadcasts on CBC. Sometimes the Canadian broadcasts cut the standard UK skit and other times they left it in and cut something else (it was always a treat for me to watch the Canadian broadcasts to see if i could catch an extra act!)
Unfortunately, i didn't start watching The Muppet Show on CBC until season 4 so i can't tell you what the original Canadian broadcast ommitted in the Joel Grey episode. Due to the "reconfiguration" of the present Canadian broadcasts (showing newer themes) they're obviously not pulling out the original tapes from the vaults so the distributing entity probably automatically cut the first act of the second half (traditionally the UK skit) or the station may be making the call (as was the case when Nickelodeon aired the episodes in the '90's - they were given the full episodes and were able to cut them as they wanted.) So if any Canadians remember watching the original broadcasts, you may want to see if you can catch some sketches you didn't see the first time around way back when!