Please be aware that London has multiple airports and that these results are for all airports serving the city.
The best day to arrive at London is Wednesday and it would be best to avoid Saturday, as prices are on average 221.61% higher than on Wednesday. (Average prices, based on 465 datapoints.)
The cheapest airline flying from London to Dublin is Ryanair. They are 58% cheaper than British Airways. (Average prices, based on 204 datapoints.)
The best time to fly is at around 18. (Average prices, based on 375 datapoints.)