What else is new?
Purple never made a secret that Bombay Calling spawned Child in Time, even at the time. Zep stole and tried to hide the truth, had to be dragged to court for the obvious etc. DP, otoh, were gentlemen or at least tongue in cheek about the whole thing. But It's a Beautiful Day even more so:
When DP were recording In Rock in 69 they all heard that It's a Beautiful Day album 24/7. The whole band loved it. Then one day Jon Lord starts jamming the song in the studio on Hammond, Gillan fools around with it, they slow it down ... The rest is history.
So they send the guys from It's a Beautiful Day a copy of the finished In Rock LP, "in case you haven't heard ...". And the guys from It's a Beautiful Day write back in good humor and say "
We heard alright and you just wait for it!!!".
So what happens? No litigation, but rather the next It's a Beautiful Day release features a song which - uncredited - is a carbon copy of Deep Purple's instrumental Wring that Neck/Hard Road. Roger Glover: "I almost fell over laughing when I heard that, It's a Beautiful Day were real sports about it".
The stolen melody starts at 1.24:
It's a Beautiful Day pay homage/get their own back at 0.35:
There is a lesson to be learned here. The whole world could be a better place if people acted like IABD and DP. And as we've mentioned sports in the above text: You don't always have to smash other people's toy cars either.
That said, there is no denying that, commercially, DP drew more from Child in Time than IABD from Don & Dewey. CIT became Gillan's vocal-artistic calling card and that organ intro which note for note copied IABD's version became signature Lord in the ears of DP fans. For decades it was a part of their set until Gillan refused to sing it anymore because he could no longer reach the high screaming parts of the original version yet did not want it transposed either (actually a bone of contention which in part led to Blackmore's departure in the early nineties because he demanded the song to remain in DP's set and Gillan refused). As such IABD would have surely had a case to go after DP, yet didn't. Pretty much unthinkable in this day and age.