It's FGW▸ (First Great Western) that are breaching their "conditions", not drivers and guards, it's over YOUR safety that these strikes are being carried out, where competence assesors who aren't actually passed out as guards OR drivers are working trains, if your train derailed you would expect a competent person to take charge of your safety.
The details on the RMT▸ (National Union of Rail, Maritime & Transport Workers) website are very limited so maybe I^m not fully understanding the situation but from what I can see on the BBC» (British Broadcasting Corporation - home page) Website the strike has been called because management have worked Sundays to cover for staff who do not want to work.
I would have thought that if the management are not fully qualify to drive / guard these services then this would have been reported to HMRI▸ (Her Majesty's Railway Inspectorate) who would have taken action?
If there is more to this then why are the RMT not providing the details to try and win passengers support?