Iran was sanctioned not for its generalised foreign policy, or for its abuse of human rights internally, or for the terrible things it has done to support the murderous Assad regime in Syria, or for what it has done in respect of the situation in Lebanon, or for what it is doing to support the Houthis in Yemen, or for its hostility to and visceral hatred of the idea of self-determination for the Jewish people and the state of Israel, but for its nuclear programme. There may be arguments for extending sanctions on Iran, but we have to recognise that, so far, this is about the current sanctions regime.
Chris Bryant is right that successive British Governments have played an important role when other Governments wobbled, or when other Governments, such as the Hungarian Orbán Government or the Italian Government—he mentioned Berlusconi, but the current Salvini Government are doing the same thing—have been complicit in being friendly to the aspirations of Putin in weakening sanctions regimes. We have stood firm, and we, France and a few others have led the way on tough sanctions.
Sometimes our EU partners have been divided and we have tipped the scales towards a more robust regime. If we are outside the European Union, that EU regime is likely to be weaker than it would otherwise have been. We would also find ourselves facing all the economic problems that come from being outside the EU, and we would be susceptible to pressure from other countries to go soft on sanctions because we would not have the collective weight of the European Union behind us.