Yes it is possible, and it's easier than it used to be. In the UK you would now need to:
1) Obtain a minimum of a EASA PPL (CAP 804 Section 4 Part Q Subpart 1 Page 5 - gives the option of with/without IR);
2) Add the ratings for which you wish to instruct, such as MEP;
3) Complete CPL Theoretical Knowledge;
4) Complete FI training as assessed at an Approved Training Organisation which runs Instructor Courses; no specific duration of flight/ground training;
5) Complete FI Assessment(s) of Competence.
See CAP 804 Section 4 Part Q Subpart 2 Page 1. This is better than it used to be, where a minimum amount of training was specified under JAR-FCL. Similar, in fact, to going EASA >> FAA except the FAA require a minimum amount of training prior to test where EASA doesn't.
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