Why is it cheaper....

[maestro1993]

For me to buy a Anytime Day return ticket from Charlton to Sittingbourne as opposed to a Anytime Day return from Sittingbourne to Charlton

 

[LexyBoy]

...Because the Sittingbourne-Charlton fare is more expensive than the reverse.

This is fairly common on commuter flows, since the peak demand is in one direction only, so a premium is paid to go this way. Often there is no difference in Off Peak fares, as there's less difference in demand off peak.

Note that it's not permitted to use the return portion before the outward (you can bin the outward and only use the return though).

 

[maestro1993]

Oh okay, thank you

 

[SussexMan]

Note that it's not permitted to use the return portion before the outward (you can bin the outward and only use the return though).

That first bit isn't right - you are contradicting yourself. You certainly can use the return portion before the outward portion but you can't use the outward portion after the return portion.

17. Using a return ticket
A return ticket (including a two-part return ticket) is only valid for the outward journey shown on that ticket if the ticket is completely unused. You may not use the outward part of a return ticket after you have used the return part.