

so in my position, the 'back-up offer' cant work rah?
also, if offered, are there any more contingent checks to be conducted (references, background), or does it mean confirm can sign and start accordingly already?
Usually when they say they want to offer you, means just wait for HR, although sometimes the HR will do a reference check (which means another day wasted)
HR will call you to give a verbal offer - X amount then ask if you accept or not, then they will draft the contract (after you accept)
But some HR take very long to get back to you, so don't pin your hopes too high. (Sometimes as long as 2 weeks)
If you want to play punk (and get blacklisted by the company that offered you, or the HR that offered you, because HR managers do move to other companies) you can accept job A, then wait for job B to offer
Do note that by doing so you can effectively
1) Forget about joining company A ever again in your career
2) Forget about ever working under the manager that interviewed you, regardless of which company he is in.