Peter Austin, managing director for London Overground Rail Operations Limited (LOROL), said:
"We are disappointed by the result of the ballot, but would highlight that fewer than half of our 124 conductors voted, and only 43% of those voted in favour of industrial action.
"We believe industrial action is unnecessary. LOROL continues to give the RMT assurances on employing conductors in alternative customer service roles and offering a generous voluntary redundancy package to those who want it.
"We urge the RMT to work with us to maintain progress in safeguarding jobs and avoid disruption to passengers."
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The 52-year-old had previous convictions for violence but was not on the anti-terror watchlist.
In a statement Charlton Athletic said: Keith was a true hero who will be greatly missed by all the Charlton family and everyone at the club.
London and the worlds has united on Twitter in defiance of the West minster attack #prayforlondon #wearenotafraid