He absolutely won't lose his job and registration, loads of doctors are on antidepressants. It's the depression talking - and the text he sent you suggests to me that he wants and needs help, he just doesn't know how to go about it.
Given his job I would be a little careful about calling 999 or depositing him at the local A&E - although if you have even the slightest concern of course call immediately, the fallout will be manageable and far better than the alternative.
But given that he is now sharing suicidal thoughts, he HAS to get help, and within a day or so, not a week or two. Don't give him any ultimatums (get help or I'll call 999), as that might just stop him from talking to you. Can you afford to go to someone privately at first, so he can feel more confident that it won't be on his record? Or even talk to your own GP about routes for getting help?
Also get some support for yourself, my DH suffered from depression when DD was a baby and it was a soul-crushing experience.
Please help him make sure something happens soon. Without wanting to e unduly alarming, medical professionals have higher suicide rates than others, partly because there is a personality tendency towards depression, a common fear of seeking help and also a knowledge of how to do it effectively. Sometimes forcing help or even a hospital visit is an act of love, even if he rages now.
Once you've decided what to do, does he have a mum or a close friend who can be trusted to help without spreading word or making hi feel too uncomfortable? My error with DH was to rely a lot on my mum, who judged him very harshly for being so out of it while we had2 babies at home (which made things hard later), and not enough on his own mum who was actually fantastically helpful and of course totally unconditionally supportive of him as well as us throughout. Good luck with getting the help you all need 