Catherine Maclean, a volunteer campaigning to keep Britain in the EU, is on the phone with a "Leave" supporter, trying to change his mind. It is not going well.
"He's a tough one," she whispers, raising her eyebrows.
She tries to break back into the conversation. "I think...," she manages, before being interrupted by a fresh tirade against the European Union.
The conversation, part of the campaign for Britain to remain in the EU at a June 23 referendum, soon strays into discussion of Turkey's process of accession to the bloc.
The man on the other end argues that it will join imminently, touching on one of the key arguments of the "Leave" campaign, immigration. Maclean argues it is a long way off yet.
Eventually, the call comes to an end. "I do think the risks are more with going out than remaining in but clearly we have a different view on that," she surmises.
"Thank you for your time anyway, goodbye."
Sporting short hair and an "I'm In" T-shirt, Maclean is one of a small team of volunteers for the "Remain" campaign led by Prime Minister David Cameron.
This evening, they have transformed an office on the 24th floor of a skyscraper in east London's Canary Wharf business district into telephone nerve centre.
Their mission is to contact as many voters as possible to try to convince them to vote for the status quo.
With less than two weeks to go until the vote, opinion polls are tight -- "Remain" is on 51 percent and "Leave" 49 percent according to a polling average by What UK Thinks academics.
- 'Desperately worried' -
The effort represents a "last push", according to Thomas Cole, the group's leader, wearing jeans and a T-shirt.
"We can be successful, we need to make sure that we galvanise our supporters," he added.
To boost the morale of the troops, there are motivational phrases and smiley faces up on a white board. These include "In it to win it!" and "Team work makes the dream work!"
There are also plenty of sweets, chocolate and fizzy drinks to keep their energy levels up.
Another volunteer, 28-year-old Sarah Barber, is trying to shoot down the pro-Brexit claim that the future of the state-run National Health Service is at risk from the EU.
Afterwards, she tells AFP that has serious concerns about what could happen if Britain votes to leave.
"I feel desperately worried about the referendum and worried that we are going to make a huge mistake which we won't be able to rectify," she says.
"I haven't done anything yet to kind of volunteer locally and I found out about this and if this is the only way I can contribute... then that's what I can do to make a difference."
Hundreds of phone calls later, the volunteers pick up their bags to go home, hopeful that their efforts may have helped keep Britain in the EU.