There are two aspects to motor insurance:
1. That required by law (essentially this covers the driver for damage or injuries he may cause to third parties).
2. Additional cover. This usually takes the form of either �Fire & Theft� additions to the policy or �Comprehensive� cover which also provides for repair or replacement of the policyholder�s own vehicle in the event of an accident.
Cover required by law cannot be repudiated by the insurers save on a few very limited grounds. Mainly this is where the driver is disqualified from driving. Third Party claims in all other circumstances (including where the car is not taxed, does not have a valid MoT or where the driver has broken the law when causing an accident - for example, speeding or careless driving) must be honoured.
Additional cover can be repudiated provided the exceptions are listed in the policy wording. I do not believe any of the major insurers make such an exception for untaxed vehicles. Mine insists that an MoT (if applicable) must be in force (though this would not facilitate non-payment of Third Party claims) , but it says nothing about tax.
I don�t know where �No Penalty Points� gains its information from, but it is wrong. I have posed a question to their �experts� and will post the answer (if I get one).