When Operation Deadlight planning began

When did planning for Operation Deadlight begin?

British planning appears to have begun around April 1945, alongside German planning for Operation Regenbogen.

The planning stage preceded the large May surrender and scuttling sequence. Both sides were already considering control or destruction of the U-boat fleet while combat continued. British planning is presented as an approximate April date, while Operation Regenbogen is placed more firmly in that month. The timing links the German denial plan to the Allied disposal problem that followed surrender.