Really?! Where are the conflicting answers?!
This is not a grey area. Being a sole trader has no effect on either spouse's entitlement to a PAYE credit.
As long as you have PAYE income (apart from as a director of your own Ltd co.), you will be entitled to a PAYE credit. Simple as that.
As long as your wife has PAYE income, she will be entitled to a PAYE credit. Simple as that.
The PAYE credit is 20% of your PAYE income, subject to a max credit of 1,650 in 2012 (which equates to 8,250 of "tax free" PAYE income).