This is a bit of a chicken and egg situation, two approvals are required, one for the individual instructor and the other for the organisation. Normally both are applied for together unless the organisation is allready approved.
You can start the ball rolling by applying to CAA PLD Standrds Support. It takes quite a while to get to the selection process which is now conducted at a Flight Test Centre and lasts most of the day as opposed to the old interview system.
Whilst you are waiting, sit in on a course and arrive well prepared with a knowledge of how to run an FICourse.