http://www.london.gov.uk/view_press_release.jsp?releaseid=2102This poll seems to contradict the earlier posted poll from the Guardian, but this is just Londoners and maybe the Guardian poll cast a wider net.
excerpt:
59 per cent of Londoners now think the military attack on Iraq was not justified compared to half that number, 29 per cent, who think the war was justified, according to a new Mori opinion poll.
The poll also found that the 48 per cent of people in the capital think that London has become less safe because of the War on Iraq, compared to just 3 per cent who think the war has made London more safe.
Also be sure to click on the link at the bottom titled "Mayor's Message to Protestors. (added on edit)