David Cameron has hailed the Newark by-election result as "very good for the Conservative Party" but he said the Tories needed to "work between now and the next election" to win back voters from Ukip, who came out second in the by-election.
The PM was speaking in Bayeux, France ahead of D-Day commemoration events.
Asked how he would win back support from Nigel Farage's party he acknowledged the challenge posed by Ukip:
"The job isn't finished yet but we are on the right track, let's stick at it."
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Officers were attending a security alert about a suspicious device close to a school being used for the European election vote.
Theresa May will meet Tory MPs’ shop steward Sir Graham Brady to discuss the timetable for her exit.
Results of the European elections will not be announced until Sunday night.