I was reading this thread as my great-grandfather was Thomas Grant, a policeman in Dublin.I have no connection with this Thomas Grant, but you should be aware that there were two police forces in Ireland at that time - The RIC and the DMP (Dublin Metropolitan Police) The complete lists of members are available in 2 books written by Jim Herlihy , and you can read them in your local public libraryThe civil marriage records are now available online via the Mormonshttp://pilot.familysearch.org/recordsearch/start.htmlwhich is not easy to use, but once you get the hang of it, it does have it all indexed.
There is a birth for Thomas Healey Grant in FreeBMD June 1865, Birmingham, ref. 6d 41Is this your man?Kooky[This is the only birth for a Thomas Grant in Birmingham, from 1864 to1866]
I didn't know there were two police forces in Dublin