IMC is a National rating and is not subject to EU Law, there is nothing to prohibit an Examiner training and testing an IMC candidate apart from "good practice".
Whopity - You are wrong.
It is the UK CAA that authorises Examiners and Examiners have to abide by the limits of that authorisation. In September 2012 the UK CAA aligned the requirements for the testing for National Licences/Ratings to match those of EASA.
Standards Document 21v2 August 2013
Section 1.2 Page 6
"Examiners are certified by the CAA ........... The privileges and requirements of Examiners are set out in EASA Part-FCL Subpart K"
= No Testing of own students.
Flight Examiners Handbook July 2014
Supplement 2 - National Licences and Ratings
Section 6.1
"Except for Microlights Examiners
shall not test applicants to whom they have given instruction"