Metropolitan Police commissioner Cressida Dick joined officers patrolling the South Bank on Saturday after the terror threat level was raised to 'critical'.
The commissioner travelled by tube to Waterloo Station and patrolled along the South Bank as the Met's visible presence in the capital was increased following Friday's attack at Parsons Green.
She said: "Yesterday we saw a cowardly and indiscriminate attack which could have resulted in many lives being lost. Again we saw a quick response from all the emergency services and transport staff.
"Since then, we have had teams of detectives and specialists working through the night on the investigation and officers throughout London mobilising and providing an increased visible police presence – especially in crowded places.
"Last night I visited the scene of the attack and our operations room and saw first-hand the complex and professional job carried out by our experts on the ground.
"London has not stopped after other terrible attacks and it will not stop after this one.
"Officers and staff from throughout the Met have been called in to provide extra shifts and yet again I am hugely proud of their response. We are pleased that there has been a significant arrest this morning but the investigation continues and updates on this will be provided as we are able to.
"I have joined officers out in central London today, meeting Londoners and visitors. It is a simple message, but a powerful one, to see London getting on with its business enjoying the weekend and everything the city has to offer.
"You can help us by remaining vigilant and letting us know if you have any concerns."