Ystwyth
Most go-arounds at LHR are caused by the aircraft in front not vacating the runway. ATC posters on this forum from LHR estimate that on average there is one such incident per day.
Unless the weather is very windy (as on March 20th this year) it would be rare to see a go around for any other reason. On March 20th a number of aircraft went around because of crosswinds out of limits during gusts.
In both instances this is a completely routine procedure for which crews are well prepared. Most modern aircraft (particularly twin-jets) have very powerful engines which can get a fully-laden aircraft off the ground should one of the other engines fail during the take-off run. Thus when a landing aircraft (lighter weight) experiences a go-around and full power is applied there is an enormous amount of power available to get the aircraft out of harm's way very quickly.