Applicants need to be outside the UK while the work permit application is ongoing - cannot therefore, switch from working holiday to work permit. Experience gained while on a working holiday does not count for experience needed for a work permit. No link between work permit regulations and immigration rules - a person who requires a visa to enter the UK still needs a visa, even if they have a work permit. An Immigration Officer can refuse entry if they believe a work permit has been falsely obtained. Maximum time for which a work permit can be valid is five years, though this is likely to be the exception.
Most contracts are likely to be for one or two years.