The German firm wants buyers to sign a clause agreeing to a potential tariff, a move Porsche said is "precautionary".
Porsche's owner Volkswagen declined to discuss if some of its other brands, including Audi, Lamborghini, Skoda, Bugatti, Seat, and Ducati might follow.
A 10% surcharge would see the cost of an entry-level Porsche 911 rising from £93,110 to £102,421.
The company's Macan sports utility and Boxster models start at about £46,000.
Stuttgart-based Porsche said in an emailed statement to the BBC: "As one potential outcome of the Brexit negotiations, there is a possibility that a duty of up to 10% may be applied to cars imported into the UK by us after March 29.
"In light of this, we have chosen to inform customers whose cars are likely to arrive after Brexit occurs to warn them that they may be affected by this tariff - allowing them to be fully informed at the point of sale and, if they wish, to adjust their order accordingly.
"This is a precautionary step in the interests of allowing our customers to plan ahead."
Bloomberg quoted Porsche as saying that it needed "comprehensive clarity" on future UK relations with "the EU very quickly".
Customers who have placed deposits on or before 17 January will not be affected by the change, Porsche said. The company has no UK manufacturing, so all its cars are imported.
Rebecca Chaplin, editor of Car Dealer magazine, which first reported Porsche's move said it was bad news for industry because it would make buyers want to delay purchases until the picture was clearer after Brexit.
''Car dealers and manufacturers need to be able to communicate the prices of cars clearly to customers - it's a fundamental of this business and the government isn't helping them," she said.
AA president Edmund King said: "Import tariffs alone could push up the list price of cars imported to the UK from the continent by an average of £1,500 if brands and their retail networks were unable to absorb these additional costs."