The group has been contributing their time, money, ideas and expertise to AAP's cause for two years.
It was a strange sight that greeted people at Trafalgar Square: A bunch of people belting out "Paanch Saal Kejriwal," breaking into flash dance and congratulating each other. It was around 8 in the evening and freezing.
Far away in Delhi, the Aam Aadmi Party had just won a sweeping mandate.
This group, which has been contributing their time, money, ideas and expertise to AAP's cause for two years, had been rooting for the party.
"It was once in a lifetime experience for my wife and me," said Ramanpal Singh, who was there with his wife and young daughter.
The entire family, he said, was busy raising funds for the party. And come counting day, they couldn't sleep a wink.
"We were up at 2.30 am just to watch elections, not cricket or a movie... I never thought I'd be awake at that hour to watch how many seats a party has won," said Mr Singh.
The AAP volunteers in the UK have been organising themselves for a couple of years. They hold regular meetings, take initiatives to get more volunteers and have launched and helped in many of the party's plans.
"AAP came up with this idea of Flame of Hope... We created a flame that represents the hope we have for India and took it to 15 cities across the UK," said IT consultant Ravi Asthana. "The idea was to reach out to as many people as we can and ask them to donate as much as they can. We raised Rs 25 lakh and I donated Rs 1 lakh."
But why would so many NRIs gave up their time, money and energy? "I was born and brought up in India. My heart beats for her," one enthusiastic volunteers asserted.
But amid the festivities, some sounded a note of caution.
"We and other NRIs are waiting for Mr Kejriwal to deliver on his promises to the people. We are watching," said another volunteer.