...asking for an 'open and honest debate' means you want to slag off the darkies without being called a racist. Our friends at the Mail use this one.
...asking for 'a grown-up debate' means you want to be allowed to peddle prejudiced bullshit but you don't want anyone to tell you off for doing so. David Cameron uses this one.
...and asking for a 'mature debate', as Phil Woolas pretends, means you want to recycle the same old lies and hatred, but hope that claiming you've got good intentions means that somehow turns your venom into fluffy bunnies.
The irony is the level of 'debate' is minimal. It's a long-winded and rather tedious way of saying "I'm not a racist, but..." - but what? "I'm not a racist, but I want to pander to racists because I don't have the intelligence or skill to be able to explain why immigration is important, relevant or necessary".