Ahh right

I really doubt you'd get away with that though! Is it shown as valid in the routing guide?
Don't rely on it existing for too long now it's been revealed here, as ATOC will now see it (although the people who update the RG are not exactly the brightest sparks doing a job that is actually incredibly complex! It took them about 2 years to remove Carlisle to Newcastle via Manchester, which they became aware of after a forum member used it and was incorrectly charged extra, he got his money back & an apology though).
Going via Crewe is rather dubious, but the correct procedure if a guard thought it may not be valid would be for them to check. They could in theory do this themselves (although I think only one guard in the whole country is conscientious enough to carry a copy of the RG with him

) or, far more likely, would be to ring control to ask them to check. Control should, in theory, have routeing guide experts on tap who could, within a couple of minutes, determine that it is in fact valid... however in reality they would probably struggle with the RG. But eventually they should figure out it's valid. It's not rocket science, but it is a bit tricky for someone who has not been trained on it to figure out for themselves. It would not surprise me if some of them look here to learn how to apply the RG!
The onus must surely be on the TOC to demonstrate that the ticket is not valid, and given that it
is valid, then I don't really see it as "getting away with it".
If the TOC did incorrectly charge and then refused to give the customer a refund and admit liability, then, to be fair to ATOC, they would confirm it is valid and this could be taken to the TOC in question. They have done this before. Of course, the "error" is then corrected (hopefully complying with the law and informing the DfT these days....)