Any concerns that affect safety should, of course, be brought to the attention of those who are best placed to address them. In most cases, this will be the employer, ie the operator, maintenance organisation, etc, but if this doesn't result in a satisfactory response, then it might be necessary to contact the regulatory authority.
In many cases, the reporter may not wish, for any number of reasons, to do either of the above, in which case for those employed in aviation in the UK, pilots, cabin crews, ATCOs, maintenance staff, ground handling, etc one other option exists, and that is to contact CHIRP where every report will be handled in absolute confidence and the substance conveyed to those who should address it in such a way that the reporter will not be identified. CHIRP is a charitable Trust so as to ensure its independence from the UK CAA and every other agency.
Therefore, if you have a concern that you think CHIRP might usefully address, why not contact them? They now have a revamped website
www.chirp.co.uk that makes confidential reporting pretty straightforward and a free App that provides direct access to disidentified reports.