A newly acquired book tells of a 'British Goliath' that I'd not noted before.
The 'Beetle' or 'Mobile landmine' (MLM) was an electrically driven remote (wire-guided) device designed by Metropolitan-Vickers in 1940 and envisioned for Demolitions, tank attack & mine clearance.
Only 50 ordered before it was finally deemed unacceptable in late '44.
Combined Operations seem to have adapted it for use in the water, either floating, or moving along the bottom. Another variant was produced with a trip wire arrangement that entangled a tank's tracks before the machine reeled itself into the vehicle and exploded.

I'm having some trouble finding a web-based picture of it, the single (very clear) image in the book is reminiscent of the Goliath but perhaps slightly smaller, with some rather unusual looking tracks.

Cheers,
Adam.