Please be aware that London has multiple airports and that these results are only for City airport.
The best month to arrive at London is December and the most expensive month to fly is February. (Average prices, based on 895 datapoints.)
The best day to arrive at London is Sunday and it would be best to avoid Friday, as prices are on average 52.37% higher than on Sunday. (Average prices, based on 255 datapoints.)
At London the most flights depart around 10:00. (Hourly flights, based on 1021 datapoints.)
From London most of the flights depart to Valencia, second best connected from London is Rome. (Daily flights, based on 55 datapoints.)