The UK has robust mechanisms to ensure that its arms exports, including to Israel, comply with international humanitarian law obligations. While some concerns will remain to be monitored, Israel has provided sufficient evidence to show its intent on complying with its obligations under international law. That's why David Cameron made the decision to continue existing deliveries, on the provision that further monitoring continues to happen.
This is a deeply damaging story showing that the UK okayed further arms sales to Israel despite "serious concerns" from the UK Foreign Office that Israel was complying with international law. After the UK raised concerns with Israel, the Israeli response's failure to give more information about specific strikes led the Foreign Office to conclude that it didn't have enough information to make a judgement. It was then approved by David Cameron, who later misled lawmakers about the amount of legal advice available, despite these outstanding concerns.