Commons Speaker Sir Lindsay Hoyle said the “eternal links” between Britain and America would be remembered by the ceremony.
In 1621 the Mayflower arrived back in Rotherhithe from its voyage taking British pioneers to the New World. Friday’s flotilla sailed up to Westminster to deliver a message to Parliament that the Pilgrim Fathers had arrived safely.
Sir Lindsay was presented with a commemorative copy of The Mayflower Compact, the Founding Fathers’ agreement for governance of the settlers, which has been hailed as a foundation of the American constitution.
“That incredible voyage to the New World, though difficult and challenging in equal measure, marked the beginning of an incredible friendship between the UK and US,” said Sir Lindsay.
“One can only imagine how excited and relieved the families and friends of the settlers must have felt when they saw the Mayflower arrive home 400 years ago with messages of their safe arrival thousands of miles away.”
Ms Pelosi said in a letter to the event: “Americans continue to draw inspiration from the courageous men, women and children who set sail four centuries ago, paving a path for future generations, and creating an enduring bond between our two nations.
“The voyage of the Mayflower captures the determination and reliance instilled in our roots by these British pioneers, which still shape the values we both cherish today.”
Her message was to be read out Christina Tribble, Cultural Attache to the US Embassy. Also Attending was former First Sea Lord, Lord West, and International Trade Minister Greg Hands.
Roger Mutton, of Thames Live, which promotes the river’s history and culture, said: “The sight of our flotilla of boats marking the occasion will hopefully spread the word that the River Thames is once again open for business.”