Registering for PAYE as a Trade Union employer

Hello HMRC, I'm writing on behalf of a new Trade Union that's registered with the Certification Officer. We are planning to employ a member of staff very soon and are trying to register for PAYE. The online registration form makes references to enter either Companies House or Charity Commission numbers - we do not have these numbers because we are a Trade Union registered with the Certification Officer. Please can you advise how we register as a Trade Union for PAYE? We can't seem to proceed on the online form and when we call the helpline the automated system hangs up telling us to register online and we can't speak to anyone for help. Thanks!

Hi Jon,
You would register as "committee run organisations" - by calling 0300 200 3200.
Thank you.