Obviously it's a matter of interpretation, usually based on the intention of the parties at the time of forming their contract...
Significance of the distinction relates to remedies - mere damages for breach of warranty, but right to either choose to repudiate the contract and claim damages / continue performance and claim damages where a condition is breached.
It's a while since I did this but here are some vague points:
* Bettini v Gye  - conditions go 'to the root of' a contract (e.g. in a contract for a shipment where time is stated to be 'of the essence', a term stating the deadline for shipment would probably be a condition)
* I have a feeling Schuler v Wickman Tools is relevant but can't remember exactly why! (try www.lawteacher.net)
* More recent approach as seen in Hong Kong Fir Shipping Co v Kawasaki Kisen Kaisha  - innominate/intermediate terms - consequences of breach only known after breach has occured etc so status of a term assessed in light of this
Sorry I can't be less vague but I don't have the time to look back through all my notes, hope that's of some help.
Schuler v. Wickman is relevant as, despite the term in breach being expressly stated as being a condition in the contract, the House of Lords held that (Lord Wilberforce dissenting) the term is not a condition as a single breach would entitle the innocent party to terminate and that can't have been in the intention of the parties. terrible decision, IMO- read Wilberforce's dissent.
also of relevance is Arcos v. Ronaasen- all about opportunistic withdrawals for breach of conditions (contrast with The Hansa Nord  QB 44)
Arcos also serves as a useful comparison with the consequential approach of the Diplock Test in Hong Kong Fir