And will I get a bad reputation within my industry if it becomes known that I went for a job largely so I could improve my own situation rather than because I wanted to move companies?
A: What I find intriguing about your question is that at no point do you seem to entertain the possibility of accepting this vastly increased salary offer and actually moving to your company's competitor - and I wonder why. Just what is it about your present job, despite your employers' apparent meanness over money, that makes you so reluctant to leave? Whatever it is, you clearly rate it highly - and that's comparatively rare and well worth a bob or two.
You may be right in thinking yourself greatly underpaid; but enjoyment of job, though not much help with the mortgage, can make you an altogether more contented human being, and therefore a far more agreeable spouse, parent and friend. You'll only recognise just how much all that's worth to you, and to your family and friends, when you no longer have it. I suspect you sense all this - hence your reluctance to jump ship - but you wouldn't half mind having a bit of extra dosh as well.
So my very strong advice to you is: don't go in for bluff and bluster If your bluff is called, you'll either have to back down immediately, looking deeply silly, or find yourself limping off reluctantly to a job you never wanted. Play it absolutely straight. Go to your employer and tell him what you were offered by his competitor. Before he can say a word, tell him you haven't the slightest intention of taking it; you like your present job enormously and went to the interview out of pure curiosity.
You'd just like to think that, when salary review time comes round again, you might find yourself more in line with the market.
And resist the temptation to imply, by even the slightest twitch of the eyebrow, 'Because if not ...'