Why? At his age and with his injury problems, McGain isn't going to improve massively like Warne did.
If we consider that no Aus spinner should even be close to an automatic selection, I'd take Krejza to England over McGain. We know what Krejza can do if the pitch gives him assistance. Not to mention he's (relatively) young, and could well have alot more improvement in him.
We should have Johnson, Siddle and two of Lee/Clark/McDonald/Hilf depending on Lee's form, and whether we want someone to perform a holding role like McDonald does. North, Clarke and Katich can manage spin, unless the pitch is a spinners paradise, in which case give Krejza a go in the place of North.
EDIT: From what I've heard about Casson's recent form, no thanks.
I think there's a fair amount of unwarranted hype over Krejza.
You do realize that the guy has only once taken 4 or more wickets in an innings at the domestic level?
In fact, in terms of his whole life, from schoolboy cricket until today, he has only taken 2 five wicket hauls? And one of those was in that crazy (Krejzy?) test match over in India.
To take 12 wickets on debut, yet still have an average of over 30 must leave one scratching ones head as to how it happened - the clue might be in that he was going for 5 an over.
They were trying to smash him to tomorrow, and lost a bunch of quick wickets...
South Africa treated Krejza with the respect he deserved in Aus - and when he went back to Tasmania, he averaged 50.72 over the 4 games he played.
His 48 first class average is marginally better than his 43 test average, and, yes, he has the ability to bowl a good delivery - but there are just so many bad ones that he'll never be a top line bowler.
Katich, North and Clarke all have better records, and are all far more inexpensive.
Why waste a spot on the guy? Make him work hard at the domestic level to tighten things up for the course of a season, and if he can take wickets without being tonked every which way (ie - average 30) then maybe he can join the conversation.
But that'd take some big improvements on his part.