Foreign Minister Alistair Burt has “condemned the indiscriminate firing of rockets into Israel” in response to attack on southern Israel on Tuesday.
The rocket from Gaza, which hit a road outside Ashkelon, is the first attack since the November 2012 ceasefire agreement.
No injuries were reported.
The Minister for the Middle East said: “I am very concerned by reports of rockets being fired yesterday from Gaza into Israel, the first such incident since a ceasefire agreement was reached on 21 November 2012.
“We have consistently condemned the indiscriminate firing of rockets into Israel in violation of international humanitarian law.”
He called on both parties to “respect in full the November ceasefire. The calm since November has been welcome - it should be built upon, not reversed."
A group affiliated with the Al Aksa Martyrs Brigade, part of Fatah, has claimed responsibility for the attack which they say they carried out in response to the death of Palestinian prisoner Arafat Jaradat.
Palestinian groups have claimed that Mr Jaradat, who died on Saturday in unknown circumstances, was tortured by Israeli Shin Bet officials while being interrogated at the high-security Megiddo prison in the north of Israel.
Mr Jaradat, 29, was arrested in February after allegedly throwing stones at Israelis.