When they can cite 'non disclosure' I believe they'll normally cancel, or 'void', the policy in order to avoid paying out.
In that case, quite apart from having to pay for your own repair costs and liability for other parties, when applying for future insurance you will have to answer 'yes' when asked "have you ever had a policy cancelled". Consequences of saying "yes" are likely to be hugely loaded premiums, or outright refusal. And that applies for the rest of your life.