IAG has £23 billion of revenue last year. Over the last 9 years their total profit was £10,000 million, partly driven from slashing IT costs.
A £1 billion fine wouldn't massively hurt a company that's made ten times that in post tax profit in the last decade, but it would cause companies to take information security more seriously.
This is the equivalent of someone on an average UK salary being fined £20.
I don't think there's a single person in the realm of data protection (or information rights in general, as the ICO is the regulator for Freedom of Information laws and Environmental Information Regulations as well) who thinks Denham has done a good job.
I've never felt any regulatory body really had the technical skills to deliver anything it was meant to do - I really wonder if there are too many public policy and junior lawyers in the ICO, and not enough deep technical experts who can rapidly investigate, fact find, and recommend prosecution or sanctions.