Anti roll bar?
Some praise them, some hate them! I personally haven't fitted one, I just sold one recently actually, as I quite like the way my Minor handles at the minute.
I think generally if your damping is good, you don't really need one.
If you mean a front anti roll bar - then only if you want to INCREASE the already understeering Minor handling !! Anti-roll bars do have a place - on competition cars - when front AND rear bars may well be fitted, and used to balance out the handling. The best improvement you can do (after uprating your dampers with SAE 40 oil) is to add some negative camber to the front end. 1/4" spacers behind the eyebolts will generally do the job nicely -but you do really need to measure each side and adjust the thickness to make the two sides exactly the same. And of course - remember to adjust the tracking afterwards!
I suppose you could put on too much negative camber....to the point of getting oversteer, and then fit a bar to bring it back to neutral handling...... Seems a bit OTT for a road car......