Do you have times in mind for the returns from Blackpool for either of these?
At a slight tangent, do you have similar dates in mind for Cardiff - Swansea?
on the 28th of March my ticket from Blackpool is open, but I have a reservation from Preston to London at 19.05, so I think I will probably take the 18.29 from Blackpool
on the 2nd April I've got a reservation for the 08.45 from Blackpool to Manchester, the 10.27 from Manchester to Birmingham and the 12.30 Virgin train from Birmingham to Euston.
As for Swansea to Cardiff (ahem) I await news from our Correspondent From The Valleys - but there's no rush. Booking won't open for another three or four weeks.