The Home Office has not made an estimate of this particular figure. Applicants may apply for settlement if they meet the qualifying criteria, or to extend their stay in Tier 2 up to a maximum of six years, or to switch into another immigration route for which they are eligible.
The Government announced in 2012 that from 6 April 2016 Tier 2 visa holders who apply for settlement in the UK will be required to meet a minimum annual salary requirement of £35,000. PhD level roles and those in shortage will be exempt from the £35,000 threshold.
The Home Office published a full impact assessment on the changes to Tier 2 settlement rules when they were laid before Parliament on 15 March 2012. This is available on the gov.uk website at: