medod,
You are mixing up ab initio with basic.
On the ab initio, or primary as the RAF called it, later elementary, the Tiger Moth was replaced by the Percival Prentice with the Chipmunk only going to the reserve schools and UAS's. The reserve schools were phased out in 1953 and a large number of Chipmunks were declared surplus. When the Provost T1 came along, (the Piston Provost) it carried out primary AND basic until the advent of the Jet Provost T3, which did the same. At various stages of the RAF flying training system they have introduced, withdrawn, re introduced, withdrawn and reintroduced an ab initio, or primary, stage on the Chipmunk when it became too expensive to discover that someone was unsuitable half way through the Jet Provost stage. Re introducing a primary stage on a simple piston type solved this.
The Bulldog replaced the Chipmunk in the UAS's in 1973/4 but I don't think was ever used by the RAF as a genuine primary trainer, apart from the period when the UAS's were used as the elementary stage. The RAF did use it in the RNEFTS to train potential RN helicopter pilots. Complicated this training business isn't it.
Then the Tutor replaced the Bulldog as a genuine elementary trainer and as a UAS/AEF platform, which it still is but this has again been complicated by the introduction of the Prefect which appears to be used as an elementary trainer as well as the Tutor...