The"Martlet / Wildcats" (from the Mk.IV ) were supplied under Lend Lease. But the earlier "Martlets" delivered 1940-42 (Mk.I, II & III) were not. The last surviving Mk.I now resides at the FAA Museum at Yeovilton.
The US built ships were returned, but there was one that had an afterlife as a carrier in a foreign navy.
Biter, laid up due to her troublesome diesel engines, was returned to US control on 9 April 1945 "as lying" at Greenock. Refitted by the USN, she was then loaned to the French Navy and used off Indochina 1946-49, before she became an accommodation ship. She was not finally returned to US control until 1965, who used her for target practice the following year.
Of the 5 surviving British built escort carriers, not subject to Lend Lease, 3 were converted for mercantile use immediately following their RN service. A fourth ship, Nairana, was loaned to the Dutch Navy between Jan 1946 and May 1948 for use as a carrier, after which she was returned to the RN and then sold for merchant service.
The final ship, Campania, retained by the RN postwar, was used as a floating exhibition ship during the Festival of Britain in 1951, touring various ports around Britain. The following year she became the command ship for the British atomic bomb tests off Australia before being sold for scrap in 1955.