More so than the financial aspect, it was the actions of the son that made even friends of Derek think twice and made Team Cameron recognise the seriousness of the story. Conway was a powerful person; they were nervous about dismissing him immediately, but there was no choice.
When the story first broke, they waited to see how it would evolve and how it played out on the evening broadcasts. The first editions were horrific, with further revelations of payments to family friends and news that expenses had been claimed for the family dog (RIP Mimi).
This was the first 1980s-style disaster that Team Cameron has had to deal with. Yes, there was the grammar schools slip-up and a smattering of misguided local councillors in questionable fancy dress. But this was different.
Everything on which David Cameron had been working for months was now in jeopardy. OK, it wasn't going to lose the election on its own, but the game plan between now and 2010 is all about perception. Voters know who Gordon Brown is; Cameron has a relatively short time to convince them the Tories really have changed.
Everything about Conway said the opposite. One Tory press officer told me: 'You could almost feel the joy of commentators. There hasn't been a good Tory sleaze story for ages and this one had it all: MP's single-mother-of-three secretary's wages halved while louche son is snapped sporting a peacock hat.' You couldn't make it up.
After withdrawing the Whip from Conway, both sides have entered a race for ultimate transparency. Cameron pipped Brown to the post by demanding expense accounts from all MPs and details of family and friends in employment. You may also have noticed a strong Tory focus on social issues.
Sure, the family/social responsibility theme was already planned, but a round of headline-grabbing initiatives shows the desire to move on swiftly.
This week the Tories talked about 'disaffected young men', to whom Tory work and pensions secretary Chris Grayling refers as the 'Jeremy Kyle generation'. Expect more social reflection in the coming weeks.
Tara Hamilton-Miller was part of the press team at Conservative Campaign HQ from 2001 to 2006. She is now a political adviser.