tHE pdf below from DWP seems to confirm that COAs are acceptable as helping to confirm Right to Work and so I presume also identity.
It would also be better if you could also supply some of the other documents mentioned to help confirm your identity.
pdf is found here:
http://www.dwp.gov.uk/docs/snap-04-documentation.pdf
101. There are customers who may not be able to produce any form of
documentary evidence e.g:
• homeless
• of no fixed abode
• travellers
• victims of disaster or
• fleeing domestic violence.
102. It should be noted that if a customer cannot provide primary
identification documents, their identity may still be verified.
103. An EOI interview must still take place and once the reason has been
identified ensure all information is recorded at Part 6 of the CA5400.
104. A holistic approach should be taken in these circumstances and a
decision made based on the information provided."
Page 23:
"Appendix 1 - Jobcentre Plus – Documentation to check Right to
Work (RTW)"
"LIST B
A certificate of application issued by the Home Office or the Border and
Immigration Agency to or for a family member of a national of a
European Economic Area country or Switzerland stating that the holder
is permitted to take employment which is less than 6 months old when
produced in combination with evidence of verification by the Border and
Immigration Agency Employer Checking Service."
