This page explains what immigration categories you can switch from in to the intra-company transfer category (Tier 2 Intra-company transfer) of the points-based system to work if you are already in the United Kingdom.
You can switch in to the intra-company transfer category if have permission to stay as a work permit holder, as long as that permission was given to you as an intra-company transferee and you are still working for the same employer when you were given that permission.
If you are not in this category, you must leave the United Kingdom and apply with a new application at your local entry clearance post.
This is the process an employer must follow before employing a person who is not a permanent resident of the United Kingdom if he/she is first required to show that no resident worker could be found to take a job.
Specific types of work that have been officially listed as ones for which there are not enough resident workers to fill available jobs. Employers who wish to hire a worker from outside the European Economic Area to fill a vacancy that is on a list of shortage occupations may do so without carrying out a resident labour market test.