United will begin daily Boston-London Heathrow service later this year, with an emphasis on premium seating. The announcement comes shortly after the launch of the American Airlines- JetBlue Northeast Alliance, which has a focus on Boston and will feature an expanded and upgraded Mint business-class cabin on JetBlue flights.  Patrick Quayle, United’s vice president of international network and alliances, said the launch date will be based on demand recovery and when travel restrictions are loosened. United will use Boeing 767-300ER aircraft for the flights, with 46 Polaris business class seats and 22 Premium Plus seats. According to the announcement, the plane features the highest proportion of premium seats on any widebody aircraft operated by a US carrier between London and the US. United currently flies to Heathrow from Newark, Washington Dulles and Chicago O’Hare. Boston would be the only UK gateway that is not a hub for the carrier.