Foreign Secretary Lord Cameron is visiting Israel following the announcement of a truce in the war with Hamas.
The former prime minister arrived in Israel amid uncertainty about when the pause in the fighting will begin.
The agreement for a four-day ceasefire in Gaza appears to have hit a last-minute snag.
A senior Israeli official said it would not take effect before Friday, a day later than originally expected.
The deal will see the release of hostages held by Hamas in Gaza, with Palestinian prisoners expected to be freed by Tel Aviv.
The lull in the fighting is also expected to clear the way for humanitarian aid to enter Gaza to ease the suffering of citizens who have been bombarded and besieged by Israel as it takes on Hamas in response to the October 7 atrocities.