Freed Ukraine opposition leader Yulia Tymoshenko told anti-government protesters in an emotional speech, "You have no right to leave the Maidan [Independence Square] ... Don't stop yet."
More top news
The Labour leader did not say whether he would maintain Britain's nuclear deterrent programme.
Ukip leader Paul Nuttall also said he would want to get rid of Sharia courts.
Over 40,000 people picked up their packs to take part in the annual marathon in the capital.