In article . com,
Sam Holloway wrote:

So what's to stop Cambridge travellers buying an Ely-London cheap day
return and using that? Does the small print prevent this?

Will the ticket offices at Cambridge sell that one?

Failing that, I guess I could always either drive to Ely (despite living
within short walking distance of Cambridge station), or buy a single to Ely,
and then a travelcard once at Ely.