Not giving up on this one!

The problem seems to be that the account is used NTLM authentication, so it is not surviving the "double hop", hence the failure for [NT AUTHORITY\ANONYMOUS LOGON].

I've registered an SPN on the target server:-

setspn.exe -A MSSQLSvc/FQDN:1433 DOMAIN\ACCOUNT

But still the problem remains. Going to try some more options and come back with the answer (not that anyone cares, I know, but for my own sanity).

Andrew