Virgin Airways flight VS25 from Heathrow to New York turned back to the airport because the laser was obscuring the pilot's vision, causing him to feel unwell.
There were 252 passengers and 15 crew on board.
Metropolitan Police were contacted over the incident, and are now conducting enquiries to establish where the offence took place. So far there have been no arrests made.
The British Airline Pilots' Association (BALPA) has said last night's attack showed more action was needed to tackle this kind of crime.
General secretary Jim McAuslan said: “This is not an isolated incident. Aircraft are attacked with lasers at an alarming rate and with lasers with ever-increasing strength. It is an incredibly dangerous thing to do. Shining a laser at an aircraft puts that aircraft, its crew and all the passengers on board at completely unnecessary risk.
“Modern lasers have the power to blind, and certainly to act as a huge distraction and to dazzle the pilots during critical phases of flight.
“We are sure the police will do everything in their power to find the culprits of this attack and prosecute them.
“We repeat our call to the government to classify lasers as offensive weapons which would give the police more power to arrest people for possessing them if they had no good reason to have them. This incident shows why this is becoming more-and-more urgent.
“Pilots across the world know how dangerous laser attacks are and therefore will join with me in commending the actions of the crew of VS25 who put their passengers’ safety first and took the decision to return to Heathrow.”
Virgin Atlantic issued a statement saying: "The safety of our crew and customers is our top priority and we apologise for any inconvenience to those onboard.
"All customers will be offered overnight accommodation and we will get them on their journey as soon as possible.”
Passengers are now expected to resume their journey on a flight at 1pm today.
#VS25 on final approach into Heathrow with a medical issue to a pilot from a laser attack close to London Heathrow ⚠— Flight Alerts ⚠ (@FlightAlerts777) February 14, 2016
#VS25 Update: Pilot who needed medical assistance was the First Officer. Aircraft is set to depart again at 13:00 GMT tomorrow. ⚠— Flight Alerts ⚠ (@FlightAlerts777) February 14, 2016
Passenger on #VS25 says those in Upper/First Class were put in the Hilton Hotel and on the earliest flight— Flight Alerts ⚠ (@FlightAlerts777) February 15, 2016