Six soldiers have died in the single worst enemy attack on British troops of the Afghan campaign.
The servicemen were on patrol yesterday when their Warrior Armoured Fighting Vehicle was caught in an explosion in Helmand.
It takes the total number of British forces killed on operation to more than 400 since the US
Five soldiers from the 3rd Battalion the Yorkshire Regiment and one soldier from the 1st battalion The Duke of Lancaster's Regiment were struck around 40km north of Lashkar Gah, in Helmand province on Tuesday.
Next of kin have been informed, the MoD said in a statement.
The soldiers had reportedly flown out of the UK on Valentine's day.
The attack represents the biggest loss of life for British troops in an enemy attack since action began in 2001, and takes the death toll of UK troops in the region to 404.
The incident is biggest single loss of British military personnel in the country since an RAF Nimrod crash, which killed 14 people in 2006.
David Cameron said it was "a desperately sad day for our country" as news emerged of the attack in Helmand.
The BBC's Kabul correspondant reported that the soldiers may have hit a roadside bomb or a Soviet-era landmine.
At Battlesbury Barracks in Warminster, Wiltshire - the home of 3rd Battalion The Yorkshire Regiment - the dark green battalion flag emblazoned with a gold lion and white rose flew at half-mast.
Two uniformed soldiers re-lit a candle which had gone out next to the barracks' gates.
The candle was first lit when around 90 soldiers from the Corunna Company, of 3rd Battalion The Yorkshire Regiment, were deployed to Afghanistan less than a month ago.
The candle - which will remain lit until the last member of the battalion returns home - was the idea of the wives and partners of the soldiers, to act as a vigil for their loved ones.
Under the candle a text reads: "This flame serves to remind us of the commitment that the soldiers of this battalion are currently making on operations.
"It will be extinguished when the last soldier of the battalion returns safely to this base."
A woman and a young boy quietly laid a bunch of pale yellow roses under the sign marking the entrance to the barracks.
Before turning to leave, the brunette woman, wearing a dark jacket and jeans, gently placed her hand on the sign and lowered her head.
A card tucked inside the floral tribute said: "Dear 3 Yorks, Tragic news. Warminster is proud and will always consider you 'our boys'. J x"
An ex-serviceman who laid a bunch of red and yellow flowers at the gates of the Warminster barracks said every death hits them hard.
Lee Thomas, 43, who lives in the town, said: "I'm just here to show my respect, it's just so sad. They're only young lads. It's just a shock. Any loss is tragic.
"I've come here because of the respect these boys have earned and deserve."
Attending the church service in Warminster, the town's mayor Pip Ridout said: "Today has been one of the worst days I could possibly have imagined as far as being mayor of Warminster.
"I just can't imagine how they (the battalion) are feeling now, knowing that they have already lost six.
"That is the tragedy - that they have only been gone three weeks and it's the largest loss.
"I have two sons myself and I can't imagine what those families are feeling."
Labour leader Ed Miliband said it was a "dark day" for UK forces, adding: "We salute all of our fallen and those who continue to serve in the face of the gravest danger. They are serving with bravery and courage and we owe them all a huge debt of gratitude."
Shadow Defence Secretary Jim Murphy said: "The professionalism of UK service personnel is unmatched and their bravery is unending"
Defence Secretary Philip Hammond condemned the attack saying "we should never forget those who have lost their lives in Afghanistan to protect our national security".
He added: "This tragic incident brings home to us the dangers that are faced on a daily basis by the men and women of our Armed Forces deployed in Afghanistan ... I utterly condemn those responsible for this incident who will ultimately fail to derail a mission that is protecting our national security at home and making real progress."
The head of the Ministry of Defence, General Sir David Richard, said he was "saddened" by the news.
"This campaign has seen many personal tragedies and we owe it to those who have made the ultimate sacrifice to recognise that their courage and skill is visible in the ever more capable Afghan army and police."
The widow of bomb disposal hero Staff Sergeant Olaf Schmid offered her condolences to the families and communities of the soldiers caught in the blast.
Christina Schmid, who lost her husband in October 2009, also raised questions over Britain's capacity to cope with further deaths.
Speaking on Sky's Boulton & Co, she said: "Naturally your mind poses that question: can we, as a country, spiritually, mentally, take these losses?
"And we are going into another spring and summer of fierce fighting again. They're still very much against us being there and aren't just going to let us go quietly."