1. Is the job & industry the same?
2. Is there a probation period?
If yes to either of these, then it could be refused. I went from Retail to Teaching and they wouldn't take into account any of my old payslips, so had to wait til I'd been in my current job for at least 3 months. Even then, not many people would let me apply whilst still on probation. Ended up with the Halifax, as they are one of a small handful who would lend to me whilst not fully permanent.
Either way you are supposed to declare any change in circumstances or it can invalidate your application if they find out. So not only do you lose your mortgage, if it's not already paid out, your house move gets delayed and you have to apply for a new mortgage which affects your credit rating.