Christopher Steele isn't a real person and Orbis isn't a real company.
They are both MI6 fronts to allow the leaking of high level intelligence information in a way that allows credibility to the information but keeps a certain amount of distance from MI6 and the Government.
The relationship between US and UK intelligence groups is very close and we were in the situation where the one of the Presidential candidates has strong links to Putin and Russia.
The US agencies cannot simply release information showing Trump to be compromised by Russia, they'd be accused of trying to influence the election.
So they ask their friends in British Intelligence, who are just as concerned about Russian influence as the US, to release the information to a respected and influential Republican (McCain) in a way that doesn't directly tie the information to the intelligence agencies but is credible enough that it's believable.
This leads to MI6 using the assets 'Christopher Steele' and 'Orbis' to release the information but as with many things surrounding the election, it doesn't go to plan.
Trumps attacks on the US intelligence agencies are, naturally, poorly received so they double down on Christopher Steele and his report but without the subtlety of the first release.
The release works, the media are all over it and to add extra credibility to the report 'Christopher Steele' goes into hiding leaving his poor cats with his neighbour.
Or I've been reading too many spy novels
That actually sound very plausible.
The British government tried to ban the media revealing his name but it was too late.
Why would they do such a thing if he was EX (ie. No longer an employee of the state)?
As a private citizen, he should have applied for a legal gagging order in the courts.