HM Revenue & Customs launched its "Mortgage Verification Scheme" on 1 September.

HMRC hasn't publicised the launch of the Scheme through the normal channels there haven't been any Press Releases issued, or any announcements on its website.  In fact the only useful reference to the "Income Verification Scheme" that could be found was one paragraph under their 2010 Budget Announcement Tax Gap, Evasion and Fraud.

“Colin Barclay, Assistant Director, HMRC Risk and Intelligence Service, said "HMRC are determined to tackle fraud wherever we can. The Mortgage Verification Scheme is an unprecedented opportunity for HMRC and lenders to work together to combat fraud in the mortgage industry."'

The Risk and Intelligence Service is the department that launched the Plumbers' Tax Safe Plan and the current VAT Campaign, and will be starting the campaigns for those who provide private tuition and coaching,  and next year e-commerce trading.
HMRC has confirmed that mortgage lenders will be providing that department with the income details included in mortgage applications, and that "this information will naturally feed in to" their risk assessment processes.

Whilst mortgage lenders will understandably be concerned to ensure that lending is based on accurate income details, HMRC will of course be keen to investigate any apparent discrepancies between stated income levels for mortgage applications and those reported for tax purposes.