Samantha Orobator, 20, from south London, has been languishing in jail since last August after she was allegedly caught with 1.5lb (680g) of heroin.
Anna Morris, a lawyer for legal rights charity Reprieve who flew into Laos yesterday, said she was concerned that Orobator had not been assigned a defence lawyer.
"She hasn't been appointed a lawyer yet and that has been our concern," Ms Morris said.
"We are concerned that any hearing may be quite quick in comparison to what will happen in other countries."
Laotian government spokesman Khenthong Nuanthasing today insisted: "The trial will be carried out fairly."
He said it is expected to be held this week but was unable to confirm a date.
Ms Morris said she has been granted permission to meet with Orobator, who is five months pregnant, tomorrow.
It was initially thought the Briton might face trial as early as today but a Foreign Office spokeswoman confirmed the hearing is now due to take place later this week.
Ms Morris said: "We are concerned about the effect of the uncertainty on Sam's well-being.
"We just seek clarity from the Lao government as soon as possible as to what exactly is going to happen so that we can advise her properly."
The British vice-consul from Bangkok in the neighbouring country of Thailand flew out to Laos yesterday to check on Orobator.
A spokesman for the embassy said: "(The vice-consul) will try to see her today.
"We are trying very hard to ensure that she does have good legal representation."
British authorities have only been able to visit Orobator for a period of 20 minutes, once a month, after learning of her arrest when she had already spent many months in jail.
There is no British embassy in Laos and the nearest is in Thailand.
Orobator was born in Nigeria but lived in south London with her aunt from the age of eight.
She lived in Camberwell and Peckham before leaving the country to travel to Ireland, Holland and Thailand.
She is understood to have been arrested at Wattay Airport, in Laos, on her way back to the UK last summer.
Her mother, Jane Orobator, a student at Trinity College Dublin, broke down yesterday as she said: "I'm just appealing to the British Government, to the Laos authorities, to just please release her.
"I just want them to bring her back to me. I'm really terrified. I have been crying my eyes out.
Mrs Orobator said she has no idea why her daughter was in Laos last summer and did not believe it when she heard of her arrest around late September.
She said the case is totally out of character for her daughter, who she described as a quiet, shy, small-built girl who looks like a young teenager.
Reprieve director Clive Stafford Smith described the legal process in Laos as "a farce".
"The trial is just being put on as a show," he said yesterday.
"She is five months pregnant, without ever having met a lawyer, facing a show trial for her life.
"If this provokes a miscarriage, the Laotians should understand that they have caused the death of this baby.
"There can hardly be a circumstance where scheduling a capital trial is less appropriate."
Phonthong prison where Orobator is being held has a reputation for beatings and brutality.
Cells measuring four square metres are used to house up to six prisoners and the daily ration reportedly consists of two bowls of pig-fat water soup and a bowl of sticky rice. Most prisoners rely on their families to deliver food.
Since 2003 at least 39 people have been sentenced to death in the east Asian country.
In Laos, smuggling more than 500g of heroin carries a mandatory death sentence.
Foreign Office Minister Bill Rammell said he will raise the case with the Laotian deputy prime minister when they meet in the UK on Thursday.
