What do Birmingham airport, the Channel tunnel rail link and the engineering conglomerate Tomkins have in common? They've all been bought by Canadians. The folks north of America's 49th parallel have no qualms about snapping up British assets, but it's a rather more complicated situation when foreign bidders try to enter Canada.

The London-listed mining empire BHP Billiton was last week obliged to withdraw a $40bn (£24bn) takeover for the world's largest producer of fertiliser ingredients, the Potash Corporation of Saskatchewan, after Stephen Harper's government declared that a foreign buyout of the vast minerals enterprise wouldn't be of "net benefit" to Canada. The aborted deal has left BHP with a $350m expenses bill.

At a Toronto press conference notable for its lack of detail, Canada's industry minister, Tony Clement, explained, supremely vaguely, that he was not convinced a buyout by BHP Billiton would create a "significant net improvement in the level and nature of economic activity" in Canada. It would not, he insisted under questioning, be appropriate to get into "exquisite details".

Potash is a potassium-based soil nutrient used in soil fertilisers around the world. The Potash Corporation employs more than 5,000 people, tapping into a vast resource of the stuff beneath the prairies. It's a lucrative business. And the subtext here is pure party politics. The prospect of a foreign buyout was hugely unpopular in the province of Saskatchewan, which accounts for 14 seats in the Canadian parliament, 13 of which are held by conservatives supporting the country's minority government. An election is likely within a year.

It's unusual for such a big deal to be vetoed out and out. But it's a reminder that many nations do not share Britain's blanket "open for business" attitude towards takeovers by foreign bidders. Cadbury, BAA, P&O, Abbey, Corus, Scottish & Newcastle, Jaguar – the list of British names that have fallen to overseas takeovers goes on and on. There's been speculation that BP, wounded by its catastrophic oil spill, could be the next to face a predator.

Former business secretary Peter Mandelson wanted tougher safeguards against foreign deals – perhaps raising the voting threshold for a successful deal from 50% to 66% of shareholders, and requiring executives to consider the interests of employees, suppliers and brands alongside the out-and-out lure of cash.

In Canada, political pragmatism rules and for sure, ministers stand open to accusations of hypocrisy. Canada has no qualms in jumping up and down about protectionism elsewhere; the country spent months furiously lobbying when the Obama administration restricted expenditure of its $770bn economic stimulus package to public works carried out by US companies.

Still, you have to admire Ottawa's chutzpah in this unblinking, unflinching self-interest. When the US bookseller Amazon wanted to open a distribution hub in Canada, the government threatened a veto unless the Seattle-based firm agreed to pump millions into various cultural activities and awards to support local literature. Amazon promptly ponied up funds and promised dedicated staff to get more Canadian content on to its website and its Kindles.

Canada also made it blatantly clear last year that CanWest, the country's media empire, would not be allowed to fall into foreign hands when part of the business filed for bankruptcy protection. It's partly down to this attitude that although Canada has endured Conrad Black, it's not been penetrated by Rupert Murdoch. This is imperfect, unfair and, at times, cynical – but could our government learn a lesson or two from Canadian bolshiness?