Blocking up ground floor internal doorway - does it need dpc? etc

[Draughtsman]

Single leaf breeze (not supporting). I dug a 100sq test hole in the ctr and found conc. below the screed so I figure using conc. blocks will be ok.

Do internal walls require a dpc?

I'm assuming it would be good practice to dig out a channel in the screed and block up off the concrete below?

Thank you