Most countries (UK included) go through clearly defined Uncertainty and then Alert Phases before despatching SAR assets in the case of an overdue arrival.
In the OP's case, a phone call to Sleap during the Uncertainty phase would have revealed he'd landed, even if some "responsible person" had requested assistance due to an unclosed FP.
Closest I ever came to a SAR launch on my behalf was on crossing the Alps from Italy into France, and having to orbit for an hour with no radio reception awaiting clouds to clear the Pt St Bernard Pass. Phoned the French flight plan number to close upon arrival at Bourg (after hours by then so nobody around) to be told I had been on Uncertainty phase
