This weekend has raised serious questuions about the robustness of the fabled datum mark alignment system. A driver reported that although the datum marks looked as though all was well,he was unable to see a set of double doors at the front of the train. This raised a real concern as to the confidence we can place in this system,and as a result the driver asked for all Cat A staion platforms to have a member of staff to enable safe despatch. This reasonable request was surprisingly turned down. The driver had no option but to refused to work under the grounds of H&S until such time the management could provide a safe working practice. Despite a DMT checking all equipment and declaring it safe and well, the E&C H&S rep has today found 3 more sites were the equipment is misaligned. Clearly this demonstraes a failure of the system. A system we can no longer have 100% confidence in. We have asked for an emergency meeting of the OPO/PTI group to discuss how we deal with these issues long term. All drivers are reminded that the H&S at Work Act states you have a responsibility for your own safety as well as that of others. Any further assistance or guidance please contact your local H&S reps.