Both sides also kept firing for two hours after the truce started on Saturday evening.
The ceasefire was declared yesterday ending a five-day clash that killed 33 Palestinian Islamic Jihad targets and two people in Israel.
But Sunday’s rocket launch presented an early test for the Egyptian-brokered truce.
Mr Cleverly said: “I welcome the announcement of a ceasefire between Israel and militant factions in Gaza, brokered by Egypt.
“The ceasefire must now be honoured to prevent the loss of further civilian life.
“The UK will support all efforts to promote dialogue and create a pathway towards sustainable peace.”
The latest round of fighting was sparked on Tuesday when Israeli jets killed three top commanders from the Islamic Jihad militant group in response to earlier rocket launches from Gaza.
Those killings set off a barrage of militant fire and the conflagration threatened to drag the region into another all-out war until Egypt led meditation.
While the calm appeared to bring a sense of relief to Gaza’s two million people and hundreds of thousands of Israelis who had been largely confined to bomb shelters in recent days, the agreement did nothing to address the underlying issues that have fuelled fighting in the Gaza Strip over the years.
In Gaza, residents surveyed the latest damage caused to their surroundings, with gaping holes left in the apartments serving as what Israel said were hideouts for senior Islamic Jihad members.
At least 13 of those killed in Gaza were civilians, among them children as young as four-years-old, as well as women.