Is a qualification required to start the Joiner skills assessment for Australian Migration

No its not mandatory. You are required to either hold your completed apprenticeship papers as a Joiner (Please note these qualifications could fall under carpentry or other wood related names) and 3 years of paid work experience pre or post qualification. So, if you are from the UK hold an NVQ3 as a Joiner or Bench Joiner you would only require the 3 years of paid work experience.

If you have no NVQ3, you are required to have a minimum of 5 years paid work experience completing Joinery tasks. It is common for clients to be assessed without holding any formal training or qualification so we use your 5 years of paid work experience as a Joiner for proof.