You are correct, there is a presumption of falsity and it is up to the defendant to prove the truthfulness of his statement. Also, if justification is unsuccesfully pleaded by a defendant, that defendant may leave himself open to an award of aggravated damages being awarded against himself(i.e. far more significant than usual). The rationale for this, is to punish a defendant who has persisted in a lie and thereby further injuring the plaintiff's good name.
As regards the issue of qualified privilege, there is no reason that I am aware why in principal a defence of qualified privilege cannot be pleaded in respect of statements made to An Bord Pleanala. Indeed, if we break down the individual elements of the qualified privilege defence it will be evident that the defence is made for situations like the one above. Firstly, there is the duty/interest test, that is whether the publisher of the statement had a duty communicate and whether the recipient had a corresponding duty to receive the information. This is not an overly burdensome standard or test to satisfy and in the above case, I doubt whether there can be any significant arguments regarding the duty/interest test. The real issue (in my opinion) would be whether the publisher of the statements acted maliciously, that is with an improper purpose. Furthermore, and somewhat significantly the onus is on the plaintiff to establish malice. This could potentially be difficult to show.
Anyway, that is all fairly academic. I would urge you to consider long and hard before pursuing any defamation action. Talk to a solicitor, if he/she is any good they will probably tell you to forget bringing an action, as they are expensive and notorioulsy difficult. Although, maybe a sternly worded solicitor's letter demanding an apology might be in order.