For what it is worth, there is a petition on official Number 10 Downing Street website to have sanctions imposed on Israel.
The text of the petition is:
Israeli must be punished for its failure to adhere to the Geneva Convention concerning the collective punishment of the citizens of Gaza. Israeli tactics are cruel, malicious and demonstrate that Israel is not interested in the peace process or a Palestinian State. They are creating the ideal breeding ground for extremism, sabotaging peace efforts and squandering the good will they have been given.
You can sign it on the Petitions Page.