The power to seize an uninsured vehicle comes from here:
Serious Organised Crime and Police Act 2005 wrote:
152 Power to seize etc. vehicles driven without licence or insurance
After section 165 of the Road Traffic Act 1988 (c. 52) insert—
“165A Power to seize vehicles driven without licence or insurance
(1) Subsection (5) applies if any of the following conditions is satisfied.
<snip>
(3) The second condition is that—
(a) a constable in uniform requires, under section 165, a person to produce evidence that a motor vehicle is not or was not being driven in contravention of section 143,
(b) the person fails to produce such evidence, and
(c) the constable has reasonable grounds for believing that the vehicle is or was being so driven.
<snip>
(5) Where this subsection applies, the constable may—
(a) seize the vehicle in accordance with subsections (6) and (7) and remove it;
(b) enter, for the purpose of exercising a power falling within paragraph (a), any premises (other than a private dwelling house) on which he has reasonable grounds for believing the vehicle to be;
(c) use reasonable force, if necessary, in the exercise of any power conferred by paragraph (a) or (b).
(6) Before seizing the motor vehicle, the constable must warn the person by whom it appears that the vehicle is or was being driven in contravention of section 87(1) or 143 that he will seize it—
(a) in a section 87(1) case, if the person does not produce his licence and its counterpart immediately;
(b) in a section 143 case, if the person does not provide him immediately with evidence that the vehicle is not or was not being driven in contravention of that section.
But the constable is not required to give such a warning if the circumstances make it impracticable for him to do so.
The "reasonable grounds" is clearly debatable both ways. It may be hard to show that the officer did not have "reasonable grounds" if he had spoken to the insurer and the insurer had stated the vehicle was not insured for business use (even though the insurer would have been liable in the event of a claim). That means the seizure may have been lawful (or at least make it hard to prove it was unlawful). However, the s.143 charge (driving without insurance) should be defendable by reference to the stipulation that the insurer must take steps to void or avoid the insurance contract.
This all smacks of target-driven policing and is thoroughly objectionable.