What's a consensus network and how does it differ from a normal network?
What kind of network are you referring to as "normal" here?
What's a triple-entry bookkeeping system?
The sender, receiver, and an anonymous third party each verify the transaction. As a result, none of them have to trust each other, because there is no single point along the transaction line that someone can forge the ledger.
Aren't pounds and dollars 'currency for the internet?' They seem to be accepted more readily than Bitcoins.
And? Just because pounds and dollars are currency for the internet doesn't mean Bitcoin isn't for the internet.
That keeping a detailed log of every transaction ever made inherently has some security and privacy concerns.
Security wise it is the most secure transaction system ever created. Yes, it is inherently not private, but nothing you do online is private anyway, so I don't see the problem here.