Ideal will rectify yes, but won’t carry out gas cert. that the landlord needs. OP failed first one so will need to come out again to sign off for the landlord the second time.
GC. No. you are wrong, mate. But you are not alone.
It did not "fail" the first one. There is no such thing as a "fail" in that context. The requirement os for a cert to be issued as a "snapshot" of the installation at the time of testing. The cert IS issued as it stands. You categorise your findings, and you either do the remedials, or the punter goes elsewhere. End off.
If Ideal attend, and agree to rectify, they have to comply with 26.9, so will be left safe.
Obviously, if the punter wants a "clean" cert, he must then pay for it - but it has to be done from scratch, as that will be the snapshot at the time of that inspection.