I don't have an answer, but think I'm getting warm! This thread is great for researching history lessons:
Though "cease fire" orders were issued on 15-16 August, the fighting
forces were uncertain that the Japanese would stop fighting so abruptly
after nearly four years of brutal combat. Therefore, the combined U.S.
British fleet remained at a high degree of alertness. However, the days
passed without serious incident as carrier planes actively patrolled
over Japan to monitor the situation and to seek out prisoner of war
facilites.
On 27 August, units of the fleet entered Japanese waters for the
first time. Guided by local pilots, the ships anchored in Sagami Wan,
just outside of Tokyo Bay and within view of Mount Fuji. A day later,
some of the fleet went into Tokyo Bay itself, though almost all of the
aircraft carriers remained at sea, ready to provide air cover "just in
case". Fleet Admiral Nimitz, who had directed much of the Pacific War,
arrived on 29 August and made USS South Dakota his flagship. Aboard USS Missouri, which flew Admiral Halsey's flag, preparations were underway to host the formal surrender ceremonies on 2 September.
Almost all carriers, hmm I wonder which ones remained? The question is which allied carrier, so it might be a RN carrier. The third fleet was swarming with US carriers, but the RN was a big part of that fleet (poor RN, generally overlooked in the late pacific war, but the victors write history - there's a film where the USN capture the first enigma machine! 
).