Malcolm Saville identifies the flaw in government plans for a register of foreign spies

Bloomberg reports:

The U.K. could require foreign states to name their spies operating in the country on a government register, under a crackdown being considered by ministers.

It's an interesting idea, but I wonder if those ministers have taken into account this penetrating observation by one of the Morton twins in the final chapter of Mystery at Witchend:

"I say," Dickie broke in, "spies are awful liars aren't they?"