Thanks folks, just left Euston for a last minute decision to go to the football.
I was on the Virgin site and the explanation was a little strange or I misread it.
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This is what confused me. It states it cannot be bought at the station. However it would seem they are one and the same
Ticket Terms and Conditions - Off-Peak Single (Online)
Route Restriction (Any Permitted)
This ticket allows travel on any permitted route.
Break Of Journey
Break of journey is permitted unless otherwise indicated on the restriction code for the journey that you are making. If you intend to break your journey, please contact us to check if it is permitted. You can always break your journey where necessary to change train.
Ticket Type
OFF-PEAK SINGLE (ONLINE)
Description
Flexible ticket only valid at specific off-peak times of the day.
Validity
Your journey must be on off-peak trains on the date specified. Off-peak times vary by route - our journey planner only shows off-peak tickets on trains for which they are valid.
Booking
Can only be booked online, in advance or purchase on the day of travel (not available at stations). This ticket can only be bought as part of a return journey, and in conjunction with either an Advance ticket, or Anytime ticket. If two online Off-Peak Single (Online) tickets are bought as part of a return ticket, it will then become an Off-peak return ticket.