For Jet Provost info, have a look at:
http://www.jetprovosts.com/index2.htm
This site states that Jet Provost T.4 XS186 at was ready for collection by the RAF on 31st January 1964. It entered service with the Royal Air Force on 10th February 1964. So I don't think that XP688 (It served at RAFC Cranwell, 1962
was the last production T4.