easyJet: Each passenger is allowed one piece of hand baggage on-board. The easyJet hand luggage size is 56 x 45 x 25 cm, including the wheels and any handles. There is no weight limit on cabin baggage.
Ryanair: You can carry one cabin bag weighing up to 10 kg with maximum dimensions of 55cm x 40cm x 20cm, plus 1 small bag up to 35 x 20 x 20 onboard the aircraft.
British Airways: The maximum size of the handbag/laptop bag is now 40cm x 30cm x 15cm (16in x 12in x 6in). The size of the additional cabin bag remains unchanged and should be no larger than 56cm x 45cm x 25cm (22in x 18in x 10in). Both bags can weigh up to 23kgs (51lb) each.
Sizes correct as of January 2017.