Using the CIEH as an example, they require an instructor to have the subject knowledge and a training qualification. The training qualifications accepted are:

• CIEH Professional Trainer Certificate
• CIEH Level 3 Award in Training Skills and Practice
• CIEH Level 3 Award in Preparing to Teach in the Lifelong Learning Sector
• Diploma, Certificate, Bachelor’s or Master’s degree in education
• City and Guilds Teacher’s Certificate or equivalent
• Level 3 NVQ in Training and/or Development

Hi D

If you undertake a "Train the Trainer" course for manual handling, this will enable you to deliver levels of manual handling training to your workforce. It's not clear from your posting which public sector you are in but it would be worth checking to see if the organisation that you select to deliver your training,delivers to the standards required by the All Wales NHS Manual Handling Training Passport and Informaiton Scheme (v2.1), which, although initially produced by the NHS, has also been adopted / adapted by some Local Authorities. It would be good standard to expect from your training provider and also assist you in the delivery / design of your own training.
Best Wishes
DenH