HGV and operator licences can be checked at:
If the transport provider claims to be a member of a trade association, look up that association on the web (Google) and the majority will have an online directory. Look up the transport provider there to verify their claims. False claims of membership to a trade association are taken very seriously both by HGV Alliance and the police.
If the transport provider claims to be a limited company, you can check the records at Companies House:
We advise all drivers to carry certifications and documentation with them in order to verify who they are and dispatchers may ask for proof of documentation at any point.