RMT general secretary Mick Cash said: "Once again this union is forced to raise a catalogue of serious safety breaches resulting from the dangerous use of fake guards during industrial action with the official safety regulator.
"RMT has warned repeatedly that the use of these ill-equipped individuals is a disaster waiting to happen and yet again the supposedly independent safety inspectorate have failed to act on those warnings.
"We now expect them to take this latest catalogue of incidents seriously and to act accordingly."
An SWR spokesman said: "Our contingency staff, the vast majority of whom being experienced professional railway men and women were fully trained for the duties they carried out on Wednesday and Thursday.
"This training was verified both internally and by an independent safety advisor.
"However, any operational incidents during the strike were reported and are being investigated in exactly the same way as when they happen during normal service."
An ORR spokesman said: "ORR is talking with South Western Railway about the issue RMT has raised."
