Well, it's been quite a journey!
I went over all the info I had collated with a fine tooth comb and took the plunge and ordered the marriage certificate for Muriel and Mr. Burrell (a marriage that I had previously ruled out). Well, it turns our that 'my' Muriel did indeed marry one Victor Julian BURRELL in 1936. They later divorced and Muriel married Albert Charles CRUTTENDEN in 1946.
This is where I have hit a brick wall; when Muriel married her final husband Cyril Frederick James SMITH in 1975, her surname was HOWARTH. I can find no record of Muriel (Alice Muriel Cruttenden as her name would have been) marrying a Mr HOWARTH.
The 1939 Register records Muriel with all five of her surnames; MULLENGER, BURRELL, CRUTTENDEN, HOWARTH and SMITH. I have certificates that prove beyond any doubt that all marriages involve 'my' Muriel, with the exception of Howarth as that certificate has yet to be found)
At the time of her (fourth) marriage to CFJ SMITH in Exmouth, Devon in 1975 Muriel described herself as a widow, Both Muriel and CFJ Smith were living (separately, not together) in Exmouth at the time of their marriage.
At the time of her death (in Exeter, Devon) in April 1980, Muriel's usual address, as show on her death certificate, was Des Salines, MAJORCA.
Given this overseas connection, I wondered whether Muriel married Mr Howarth in another country, but my exhaustive enquiries and trawls through info on the www, Ancestry, FindMyPast, etc have revealed NOTHING!!!
If anyone can shed any light on Muriel's marriage to Mr Howarth (or has any info on any of her marriages), I'd love to hear.
N/17-12-2018