Dead easy training as required plus test to get your SEP rating current.
Send it off to the CAA and they will reissue your CPL (I'm assuming the 5 year expiry of the JAR licence was June 2013).
Before you can start the FI couse you need 5 hours on type in the preceding 6 months.
There been a fair exodus of instructors recently to the airlines. So if your not a cock you shouldn't have any difficulties picking up some work.