Cyclists in London could be allowed to ignore one way streets

Do TROs override the specifications laid down in TSRGD? Specifically with regards the acceptable format or roadsigns? I was under the impression that TROs could only make use of signs as defined by TSRGD.

In this case, would it not be the case that if a car were to go down the one way street that had a one-way sign, modified to allow bicycles, then the modification invalidates the sign, and therefore the TRO, and no contravention could be considered to have occurred.

The signage needs to be in accordance with the TRO. I don't know which overrides which (if so), but in order for it to be enforceable (among other things) obviously everything has to be in good order.