One of the Lancasters modified for Operation Chastise would have served well to carry the first British atomic bomb. But it would have been too risky to use it for a solo attack.
The most effective thing would have been for the nuclear bomber to fly in the center of a conventional bomber stream protected on the flanks by Mosquito night fighters.
So far everything is reasonable, but....what would have happened to all the bombers in the stream when the bomb exploded?
The secrecy of the operation would not have allowed the crews to be informed.
Blind pilots and navigators, structural damage, in-flight collisions...
If, on the other hand, the nuclear plane had been ahead or delayed the rest of the stream, before or after the attack, it would have been easy prey for the Flak Wurzburg or for the German night fighters.
Can you imagine the Luftwaffe intelligence officer examining the wreckage of the downed plane and finding a strange sphere ticking?