As below,

If you tell them you forgot they can cancel your policy there and then. non refundable and your have to take another policy out for the rest of the year.

They could cancel and refuse any insurance again

They could just add it to the policy and renew it asking for more on top.

Also if you did have a crash and this was discovered when exchanging insurance details you would not be covered and police would take what's left of your car, no pay out and your got to court more points a massive fine and worst case scenario few months in prison.

they are not completely innocent though

DVLA as a requirement ask that all insurance companies check their customers insurance against their database on a regular basis for anything such as points and disqualifications.

It is a requirement that they check it.

You can dispute this through DVLA if the insurance company threaten you with a lawsuit as it is classed as fraud.