The Gas Safety (Installation and Use) Regulations 1998 ACOP states that:

by a person who has successfully completed an industry-recognised training course followed by assessment of competence. Training that leads to assessment of competence in safe gas work should be recognised by the industry’s standards setting body; or

If there is mechanical maintenance technicians carrying out gas works on your site that are not specifically trained and authorised to do so I'd suggest that you would want to put a stop to this as a matter of urgency and have a qualified gas engineer carry out a full inspection of the system.  

Hi
John's answer is correct. You may also wish to ask maintenance why the pipework and tools are developing leaks, as gas leaks should be rare - it sounds like you need to resolve why the leaks are occurring. Like the repairs, a Gas Safe Registered Gas Engineer should be used to rectify.
Do you know how they are detecting, repairing and testing for leaks? I am guessing they are probably not doing this with a proper soundness test.

What is the process when a leak is suspected? Is the pipe work/tool isolated from the supply?

Ian

Thanks for the comments all. I informed our maintenance team on the day of my post that I was stopping them from undetaking any more gas related activities.

Following my investigations I have sourced a competent company to inspect all pipework etc and gas storage tanks. I have also arranged for our engineers to begin gas safety courses which takes place next month. Furthermore we are introducing inspection criteria and PPM for all gas related equipment and installations.

Thanks