Both the HS125* and BAe146/RJ have ‘T’ tails, but apparently for different reasons. *(125 original design)
The 125 design followed on from the Trident where a ‘T’ tail enabled rear mounted engines.
The BAe 146 used the ‘T’ tail to enhance the fin effectiveness in the four engine design. It may also have required the advantages of a high tailplane/elevator with a high lift wing (as #14, also cf YC14/YC15, C17).
Both the 125 and 146 were predicted to have deep stall characteristics, but none were found in flight test.
Both aircraft could establish an angle of attack greater than the stall angle with a dynamic entry and to a lesser degree by continued elevator input; however, no significant (unexpected) loss of elevator effectiveness was seen nor any tail blanking leading to a locked in condition. Both aircraft were test flown with stall/spin recovery parachutes.
Both aircraft had stick push systems which reduced the development and certification risk. This also enabled the basic stall speed to be established relatively quickly, and thence all of the certified performance speeds.
Also note the Vampire/Venom’s apparent low set ‘T’ tail (??!) vs the high set Sea Vixen. The latter stalled relatively normally without wing/fuselage blanking, and it was above the jet wash. Then cf Sea Vixen vs Javelin; I don’t know the reasons why the choice of tail position or any advantages other than for transonic performance.
Much of the early research into jet / swept wing tailplane position was flown by the Shorts SB5 which could be configured with either a low set or high ‘T’ tail.