Thanks Wehey.
Hmmm! I've had a look online. There seems to be more success than failure with this product but I'm unsure.
I'd quite like to give it a go a temp fix so I can keep driving whilst I prepare for a gasket change but not if it will prevent said gasket replacement by gluing the engine block shut or otherwise damaging the engine which may yet be reparable.
Any views on this and similar products?