I know this has been discussed few times, but just a slightly different case here and any advice would be appreciated.
Here is the situation.
I have accepted offer from company 1 and will be joining them soon. I am currently interviewing with Company 2 which is one of the worlds most prestigious firm and my first choice.
Company 2 doesnt know that I have an offer from Company 1 and that I have accepted it.
It is not possible for me to delay Company 1's joining and the time is too short to complete interview processes with Company 2 before I join Company 1.So in all likelihood I may have an offer from company 2 after I join company 1.
If that happens or I know that is going to happen, should I advise company 2 that I am with a new employer however they are my first choice (I have compelling reasons for this) if I get an offer. Or should I just not say anything ? But this may show up in the P45 which will be from a different employer.