I was at the same place yesterday, and it was very busy until early afternoon. I understand there is/was ATC industrial action in Europe somewhere, meaning more aircraft are departing with slots than usual. This seems to have had the effect of 'bunching' departures.
Still, Luton is extremely busy with biz-jets. It's not abnormal to see over 100 different aircraft during one day! Net Jets alone had 20 or so departures yesterday.