One of two soldiers killed as the Afghan people went to the polls was part of reinforcements sent to the country three weeks ago to boost numbers after a wave of casualties.
Defence chiefs sent 125 extra soldiers at the end of last month to maintain troop levels after a record number of injuries and deaths in July.
The soldier, from the 3rd Battalion The Yorkshire Regiment, is understood to be the first of the extra service personel to be killed.
The two soldiers, the second of whom was a member of the 2nd Battalion The Rifles, were on a patrol unconnected to election security when they were killed yesterday, officials announced today
Their next of kin have been informed.
The deaths bring to 206 the number of UK troops killed in the country since the conflict began.
Lieutenant Colonel Nick Richardson said: "It is with deep regret that we report the death of two soldiers in Helmand Province. Our deepest heartfelt thoughts and sympathies go out to the bereaved family, friends and comrades of these brave soldiers."
Earlier Foreign Secretary David Miliband hailed the "enormous bravery" of the Afghan people who defied Taliban threats and voted in the election.
Yesterday's landmark elections to select a new President were marred by a series of attacks but violence was not as intense as some had feared.
Before news of the deaths was announced, Mr Miliband said that he had been "braced for the worst" but "the worst did not happen".
He told BBC Radio 4's Today programme: "I think we were all braced for the worst after the very difficult six weeks in the run-up to the election.
"The worst did not happen yesterday but we don't yet know how good it was in terms of the ability of Afghans to come out and vote.
"We know that millions did and that millions... have testified to enormous bravery in coming out to vote, but we don't yet know the scale of the turnout."
Mr Miliband added: "What's vital is that there is a credible Afghan government to which Afghans can commit their loyalty."
Election workers were today counting the votes cast, but initial results are not expected until tomorrow.
Turnout varied widely, but early reports suggested it was weaker in the turbulent south, casting doubt on whether current president Hamid Karzai will get the 50% of votes he needs to be re-elected without a second round.
It was a mixed picture in Helmand province, where many British troops were killed or wounded in operations to provide security for the elections.
British troops kept away from the polling stations to avoid the perception that they were orchestrating the vote, but in many places they had a busy day carrying out security operations.
Lieutenant Colonel Richardson, spokesman for Task Force Helmand, said: "Where the insurgents have attempted to disrupt the elections in Lashkar Gah, the security plan led by the Afghan national security forces has had significant deterrent effect.
"The population of Helmand province have been free to vote if they so desired."
Mr Karzai has engaged in intense behind-the-scenes bargaining with his presidential rivals, but the result could rest on how well the vote holds up among his Pashtun support base in Afghanistan's troubled south and east.
Prime Minister Gordon Brown thanked British forces for their work to ensure the elections could take place despite the "major sacrifices" made in recent weeks.
Speaking to the BBC, he said: "What we are seeing is the first elections that Afghanistan has organised for itself in 30 years.
"But what we have also seen is a massive attempt by terrorists to disrupt the electoral process, to prevent people from voting, indeed to intimidate people from voting, and I want to thank our British forces for everything that they have done to make sure that these elections can take place.
"This has been a very difficult summer, with major sacrifices and major losses as a result of the campaign by the terrorists."
The body of the 201st soldier to die in the country, Sergeant Simon Valentine, 29, was flown back to RAF Lyneham in Wiltshire this morning alongside those of Lance Corporal James Fullarton, Fusilier Simon Annis and Fusilier Louis Carter, all of 2nd Battalion Royal Regiment of Fusiliers.Reuse content