Jaguar has lifted the limiter of the XJ and in doing so uncorked 174mph from the big British limo. To celebrate, the company has had world record hurdle-meister Colin Jackson hit top speed in the thing on a proving ground. It’s an epic(ish) photo opportunity. The link is that Jackson is an ambassador for Jaguar’s Academy of Sport, which provides funding to promising young athletes.The Speed Pack is an extension of a new Sport Pack for the XJ Supercharged, allowing the 503bhp 5.0-litre V8 engine to take the car to 174mph instead of the usual 155mph. It’s done by altering the car’s software, and nothing more.