Researching the issue, it’s not as bad as the impression I was left with after reading the article on BBC, who got it from The Sun.
The actual problem seems to be that if you apply a screen protector before recording your fingerprint, then pattern of the screen protector itself gets recorded as if it were a fingerprint. Subsequently when another person touches, if the screen protector is still there, the phone unlocks.
So although it’s an embarrassing bug, it doesn’t necessarily mean somebody else can just take somebody else’s phone, stick on a screen protector and unlock it. Presumably, the only precaution needed is to make sure you record your fingerprint with the screen *naked?
*Stress, that’s the screen naked, not the user.