When people have found glitches on websites before and bought something like a plasma screen for £10.00 instead of £1000, I'm sure the companies have wriggled out as the price on display is seen as an 'invitation to treat'.
In this case, because everything is done online (to save money), you enter details, pay cash & the system generates the policy - I reckon that as soon as a real person discovers the glitch, they'll have letters in the post cancelling all the policies.
If these letters were put in the post Friday, you could find yourselves driving uninsured for the weekend - or they may allow you a few days' grace & refund you pro-rata.
And they'll probably use the excuse of a malicious hacker...