Don't forget that this web site has a a page devoted to UK productions with a list of all current ones. All the information about this production is on there.
Lynne
I should have added perfs are 18 to26 Oct (not 20, 21 Oct) Eves 7.30 Sat 26 at 3. Box Office at Cochrane 020 7269 1606
This is not a recommendation, just info.
Merrily at the Cochrane is a student production by Mountview Academy. Of all Sondheim, Merrily is probably best suited to students and the notable first London prod was from LAMDA.
My memory, supported by a poster on the wall, says the European premiere of MWRA was by the Guildhall. I caught it at the Bloomsbury in 1983. It was certainly notable.
I think you are right about this being the first European production. The first professional one was in 1984 at the Library Theatre in Manchester and was so successsful they did it again a few months later ! Michael Cantwell was Frank and Tracie Bennett was Mary. Incidentally it was the first Sondheim production I ever saw.