Please be aware that London has multiple airports and that these results are for all airports serving the city.
The best month to fly between London and Barcelona is February and the most expensive month to fly is May. (Average prices, based on 207 datapoints.)
The best day to arrive at London is Tuesday and it would be best to avoid Monday, as prices are on average 431.38% higher than on Tuesday. (Average prices, based on 326 datapoints.)
The cheapest airline flying from London to Barcelona is Vueling. They are 64% cheaper than British Airways. (Average prices, based on 218 datapoints.)
The best time to fly is at around 21. (Average prices, based on 296 datapoints.)