Irrespective of WHY this was done the following facts still stand.
The journo was airside without proper authority/security clearance - deal with that appropiately as with any other person airside 'illegally' would be.
The driver is in contravention of the terms which accompany his airside pass issuance - withdraw it immediately and ensure he is prevented from ever holding another.
Consider banning all this company's vehicles and staff from airside until the result of the enquiry and a DETR inspection confirming appropiate security measures are now being followed. Tough on their employees and the airlines involved, but perhaps the company can pursue damages/losses against the driver. And it might stop other idiots doing things like this.
The photos in the 'paper' could have been taken just about anywhere, or by a pax boarding or from over the perimeter fence, which incidently would put you closer to landing/departing aircraft than most of the airside roads would permit.
There are much easier ways of 'attacking' planes and there are loopholes ,(at LGW and other airports), of varying sizes which again would provide easier airside access.
View From The Ground - I also thought exactly the same thing - I wouldn't wish that on any police officer though as I m sure (s)he would be made a scapgoat - especially by the press.