Mark Thomas is joking of course, but the joke makes no sense unless you believe that companies relocating to Jersey would be forced to stay in Britain if the option were removed. Other choices such as Switzerland, Asia or the Americas (or just going out of business) do not occur to him. He has been touring Britain asking audiences for suggestions for government action with disturbing results;
One of my favourite ideas was the simple proposal that "Britain should invade Jersey". Now that TV's Bergerac is just a distant memory this policy has become truly popular, not least because Jersey is one of the tax havens that have become the legal pirate coves of the 21st century. The Tax Justice Network (not to be confused with the rightwing Tax Payers' Alliance) estimates the UK loses about £18bn a year in tax revenue due to "corporate tax efficiency" ie companies moving offshore. The Iraq war cost at least £8bn. So war with Jersey would not only be morally right but self-financing too. In fact we could probably do a bond issue for the invasion to pay for everything up front with the promise of a steady yearly return for investors.
Unless people are enslaved, they can always relocate themselves and their businesses. Rolex was a British company until the words "Made in Switzerland" on a timepiece acquired such cachet that they couldn't compete. Mark Thomas presumably thinks it would have been better for the company to die, wrapped in the Union Flag. When did Colonel Blimp get his commission from the KGB?
Note how, in accordance with the Guardian style book, the Tax Payers' Alliance cannot be mentioned without the damning words "right wing." Note also how easily the contradictory words "legal" and "pirate" sit together in a Guardian sentence, as long as the "pirates" make wealth, rather than take it by force in the traditional manner, as governments do. Note also that all wealth not collected in tax is deemed "lost" to the nation, as opposed to merely being spent or invested by those nasty grasping types who made it.
I strongly suspect that Jersey would be even sleepier, and there would be many more, and more prosperous, businesses in mainland Britain, if our taxes were reduced to levels that would shock Mark Thomas and his audiences. God knows how much wealth is truly "lost" to Britain because never generated in the first place due to the disincentive of excessive taxation. We shall probably never know as long as Mark Thomas and his audiences are such fools.