Bunking off

Not to be confused with bunking up.

Although there is nothing stopping you from having a bunk up while you're bunking off.

I assume it's an English (cockneyish) phrase for being a bit moody.  hence "long live hookey st" in the only fools song

I see from urbdic and wiktionary that I am wrong.  does make me wonder where that lyric came from tho.

skiving

What JC said

I’d always heard the Only Fools lyric as “long live Cookie Street.”

In Oz it’s called wagging

no idea why 

It was called wagging at my school as well (which was not in Australia).

Having looked it up it seems the derivation is from an old term for mischievous boy.

At my school it was called shirking.