By Chiara Fiorillo McDonald’s is slashing the price of two menu favourites – but the offer is available for a limited time only. Fans of the fast food chain will be able to get a Big Mac for £1.49 on Monday, saving £3.50 from its original price of £4.99. And if you go to the restaurant in the morning, you will be able to buy double McMuffins for £1.99. The deals are only available on February 26 through the McDonald’s app. The company said: “Customers will be able to earn points when they purchase one of these deals by opting into MyMcDonald’s Rewards. The scheme means every penny spent equals…