Prince Edward also attended the St Paul's service, which was organised by the RAF Association.
The Venerable Jonathan Chaffey, Chaplain-in-Chief of the Royal Air Force, gave the address and told the congregation that on September 15 1940 - regarded as the turning point of the Battle of Britain - Air Vice Marshall Keith Park famously told Churchill there were no reserves.
He added: "The Battle of Britain however is not about a single individual, it is right first of all to honour the few who daily took the fight to the enemy.
"Reading some of the pilots' memoirs, one suspects that they themselves were running on empty by the 15th of September, having given all."
Outside the cathedral were dozens of Polish people or those of Polish descent, waving their nation's flag, and the Chaplain-in-Chief highlighted the contribution of fighter pilots from Poland, saying their gallantry was applauded at the time as "unsurpassed".
He added: "The message is clear - the Battle of Britain is a story of a whole force working together in a crucial cause."
During the service, David Cameron gave a reading from the Bible,recounting the story of Jesus's disciples arguing about who was the most important.
The Chaplain-in-Chief returned to the story during his address: "This idea of sacrificial service for the common good is as important today as it was 75 years ago but it has always been a difficult one to learn. Even the disciples of Jesus struggled.
"When they started a quarrel as to which of them was the greatest follower, Jesus needed to remind them true leadership is not about power but rather service. If anyone wants to be great he must first be the servant of all."
A scale-model Spitfire was positioned at the west front of the building to commemorate 'the Many' who supported 'the Few'.
Bishop of Portsmouth, Rt Revd Christopher Foster told Premier there was significance in remembering the event as part of collective worship.
"Remembering is not simply an individual thing. Of course, those who directly remember the events then are few in number now. But there's something terribly important about collective rememberance," said Bishop Foster.
The largest collection of Second World War planes are taking to the skies later since the conflict itself, when on this day in 1940 the Germans lost 61 of their own aircraft.
Jeremy Corbyn attended the service at St Paul's Cathedral as he was embroiled in a row over his pacifism after refusing to rule out wearing a white poppy on Remembrance Sunday.
The Stop the War Coalition chairman said: "My mum served as an air raid warden and my dad in the Home Guard.
"Like that whole generation, they showed tremendous courage and determination to defeat fascism. The heroism of the Royal Air Force in the Battle of Britain is something to which we all owe an enormous debt of gratitude.
"The loss of life - both civilian and military - should be commemorated so that we both honour their lives and do all that we can to ensure future generations are spared the horrors of war."