Probably not the best practice... Do they operate their own forum No names...There is a company in the UK, MCS registered, who have been issuing MCS certificates if you buy from them.
@Shunterwork, I understand that you work on the solar side though up till now on roo-fit scale projects, the MCS regulations work very much like PartP etc, putting a lot of onus on the MCS registered "INSTALLERS", as such they could be letting themselves open to losing that registration for various non-compliances. So in most cases they wont do it.
See here: Microgeneration Certification Scheme - Installer Standards