To be fair (if only briefly) the newly discovered memos only say that:
'We were determined to get a fair slice of the action for UK companies in a post-Saddam Iraq'
Nothing in the article says that we went to war because of oil (that doesn't mean we did or we didn't - it's just that the article doesn't help either way), what it says is - having spent UK blood and treasure invading the place isn't it reasonable that UK should get a fair share of the rewards?
I accept that I am a bluff old traditionalist, but that doesn't sound like big news to me. A 'leaked' memo showing Tony B had said 'the oil is why we are invading - I made up the WMD thing to fool everyone' would be interesting; this is not.