Jo Swinson has said if she was leader of the Liberal Democrats the party would work with other parties and put up joint candidates that support a second referendum.
Swinson said that Remain voters want politicians to put aside differences between parties and work together to stop Brexit.
At the European elections pro-Remain parties were criticsed for not working together to compete with Nigel Farage’s pro-Leave Brexit Party.
At the Peterborough by-election there had been plans for a Remain unity candidate, but the plans fell apart at the eleventh hour.
Swinson said she would look again at the issue if she becomes leader of the Liberal Democrats.
By contrast her rival Ed Davey appeared to dismiss the idea by saying: “Anyone on our side who suggests a pact would be selling the Liberal Democrats short. A pact would simply blunt our clear anti-Brexit, pro-environment message.”
Speaking to the Times, Swinson said the overall result in Peterborough was “a good example where different parties that do all believe in stopping Brexit decided that we could work together to put forward a united front”.
She said that voters with concerns about Brexit “want politicians to be able to work with one another and to look beyond their individual party loyalty and interests to the wider interest of how we can stop Brexit”.