My company allowed me to start a type rating having only the IR current (MEP lapsed by a few weeks) The only proviso was that the MEP had to have been either attained initially, or revalidated within the past 2 years. Wether that was a company policy or a CAA one is beyond my limited knowledge. The only real pre-requisite for an initial Type Rating is a current IR, as far as I am aware.
hope this helps