I'm only repeating what they're saying on FB - that's now the second time they've got it wrong then. You're saying it has to be on in the next month then?!
Well Amazon UK definitely say I can buy it on 5th November and BBC4 has the exclusive rights to Spiral in the UK. Sky never allowed any DVD's before they had shown there latest series on Sky 1. Plus foreign drama shown on BBC4 is always followed by the DVD's.
Either way you do not have to wait until January 2013 to view it.
It may follow Montalbano. The UK Montalbano DVD's are released after the episodes are shown on BBC4 too. I suspect October or late September as it runs for four two five weeks, if their showing two per time.