Yep — big difference:

UK (Gruinard Island):

Tested anthrax in WWII

Publicly acknowledged

Quarantined for decades

Decontaminated by 1990

USSR (Vozrozhdeniya Island):

Secretly tested smallpox, anthrax, plague

Denied everything

Caused a deadly smallpox outbreak in 1971

Covered it up for years

One island had warning signs. The other had a cover story.> The UK, meanwhile, made it very very clear which island they used for their anthrax testing in WW2.