Please be aware that London has multiple airports and that these results are only for London Gatwick Airport.
The best day to arrive at London is Wednesday and it would be best to avoid Friday, as prices are on average 128.33% higher than on Wednesday. (Average prices, based on 207 datapoints.)
From London it is on average the cheapest to fly to Madrid and to Istanbul. (Average prices, based on 99 datapoints.)
From London most of the flights depart to Amsterdam, second best connected from London is Dusseldorf. (Daily flights, based on 67 datapoints.)