If you provide them with an NARIC certificate it would be easy for them to verify your degree's authenticity. I would suggest you get a NARIC certificate and post it with your application.
The HSMP Guidance document states:
"Points will only be awarded where specified evidence is provided to show that you have been awarded the relevant academic or professional qualification from an accredited institution (See the glossary for definition).
Accredited Institution – A place of study that is recognised as an institution of higher education by NARIC (please see below). Professional bodies must be recognised by the equivalent UK regulatory authority."
If you decide to send without an NARIC certificate, make sure that it is equivalent.