Hi Ian55,
I have been chasing down McRitchies in Perthshire for a short time, looking for antecedents of my 4th great grandfather, George McRitchie (abt 1781-1863) who was a baker at Strathallan Castle, Blackford Parish. The record of his death in the statutory registers gives his birth as Dunkeld and parents as John McRitchie, baker (dec) and Janet Reid (dec) (329/00 0025 Auchterader) Interestingly, George was also married to his first wife Martha Trench or French, in London in 1803 -- this marriage occurred at St Saviours, Southwark, London.
When I noticed the similarities with your Constable/McRitchie marriage, I began to look at the OPR births for Margaret McRitchie Constable's children... the Dundee parish births at this time often record the namesake of the child... no disappointment there, William and Margaret Constable's daughter Janet b 21 Oct 1807, was named after "J.Reid, grandmother". ( 282/00 0090 0283 Dundee)
So it is possible that your Margaret McRitchie Constable was a sister of my George McRitchie, and that they were both in London at the same time.
George McRitchie and his wife Martha also moved back to Scotland by December of 1812, when the birth of their daughter Mary is recorded in the Muthill Episcopal Records, and their address is given as North Gate Strathallen House, Blackford Parish, Perthshire. My 3x great grandmother, Margaret McRitchie, and at least 4 other children were born there as well, before Martha died (between 1820 and 1822). George then remarried to Ann Sorley, and he is listed in the statutory deaths as widower of Ann.
I should mention that Georgina Constable is recorded as being named after her maternal grandfather in the OPR births (082/00 0090 0523 Dundee), whereas the father's name as recorded on the statutory death register for my George McRitchie, the baker, is John. It is possible that two McRitchies could have married two J. Reids and had children in Dunkeld. However, it is also possible that the name John was reported incorrectly. William McRitchie, the son who reported George's death, was born about 1817, when his own father was nearing 40, and may never have known his grandparents personally.
Although I suspect kinship, I have not been able to locate records to positively identify the name of the father and siblings of George McRitchie, the baker. My research is conducted from afar, which complicates matters! I will let you know if anything develops, and please let me know if anything turns up on your end.
Thanks-
Gener8or