Very sad answer to your question! Sad in that I knew where to look for the answer!!!!
AP 1358 chapter 8 says;
In no circumstances are medals awarded by private societies, other than those mentioned in subpara b, to be worn with uniform.
To save you having to look it up, here is sub para b
b. The medals of the Royal Humane Society, the Stanhope Gold Medal awarded by that body, the Medal of the Royal National Lifeboat
Finally, to answer your specific question
0852. The regulations for wearing foreign insignia and non-military medals with evening uniform are the same as for wear with day uniform
The wait for OP HERRICK and OP DITTANY medals is because we are waiting for the reissue of the DCI (or should it be DIN), which is expected "in a couple of months". Expect to wait some time after that for the backlog to clear.