Retention Bonus / Leaving

[jon86]

" A retention bonus of £x will be paid upon the successful implementation of Project Z, not before September 2016."
...

I think that "not before September 2016" is referring to when the payment would be made, not specifically as to whether you're eligible for the bonus if you leave before September 2016.

... guaranteed bonus to be paid on completion of project, but payment won't happen before September 2016. Nothing mentioned about your employment situation.

Indeed. You need to read the fine-print of the clause / employment contract. It may be that you can leave before September 2016 and still be paid the bonus in September (under the 0T tax code, for example), but I would expect that any HR department worth their salt would have already made this point abundantly clear in the contract / documentation that you presumably signed.

but he's not posted his employment contract so you don't know that there isn't a general clause regarding bonuses in there, he's posted one line re: when payment would be made for this particular bonus and he's referred to it as a retention bonus which certainly suggests that it won't be paid if he leaves

if it was just for the completion of the project then the additional condition of not being paid until September wouldn't be spurious

Indeed. More details are needed before it is clear either way.