The pair, together with their professor from Imperial College London, were on a routine academic trip to study earthquake activity in the country.
They had sought the usual permission from local officials but this was delayed by the Olympics. Instead, they obtained visas using an invitation from the China Seismological Bureau in Beijing.
The two students, a PhD student aged 23, and a Master of Science student aged 22, travelled to Aksu prefecture for their study.
Aksu is one of the most tense areas in Xinjiang, where many of the local Muslim Uighur population are hostile to Chinese rule.
A series of lethal attacks in Xinjiang were ascribed to separatist terrorist groups during the summer, particularly just in advance of the Beijing Olympics.
Altogether 24 people were killed, mostly paramilitary police officers and other security officials.
Ten days into their study, in September, they were approached by local officials – believed to be from the feared State Security Bureau – the internal security apparatus. They were questioned at a hotel for several hours before their GPS devices, together with their survey results and data, were confiscated.
In a statement released yesterday (Monday) by the Aksu Land and Resources Bureau, the authorities seemed to accept they had an innocent explanation.
But it said they had collected "illegal data" from 6,000 points that was valuable for mineral prospecting and topographical research.
Mapping, like other seemingly innocent activities, is regarded as a threat to state security by the Chinese authorities, particularly in areas that are politically sensitive.
Most forms of mapping and many forms of scientific research, such as testing water supplies, are illegal unless carried out by the government, and there are periodic crackdowns.
The students' supervisor, Dr Jian Guo Liu, a Reader in Remote Sensing at Imperial College, was in another area of China at the time but maintained contact with his charges by telephone. He said he has been taking students to the area to study geology for nearly 10 years and has never encountered any problems.
"This time, we only had an invitation from Beijing and not the proper local documentation which we hadn't been able to get because of the Olympics," he said.
"We considered not going but everything was booked and the study was crucial field work for my student's PhD."
He insisted that the GPS data the pair gathered could not have been used for mapping, and that the large volume of data was mostly collected by a previous student who had not cleared it before handing it back.
"We agree that they didn't have the proper paperwork but they didn't do any mapping work," he said.
"The Chinese are very sensitive to foreigners working in that region but it's their country, what can you do?"
The two students were fined roughly £1,000 each and flew back to the UK on October 2, although an official report into the incident has only just been released.
The university is now reviewing its field trips to China. "We do these studies to help understand earthquakes, it's for their benefit," Mr Liu said.
"Unfortunately it's very unlikely I will get permission to take students back to the area for the time being."
Royal School of Mines (entrance and the Goldsmiths' wing, Prince Consort Road, London) comprises Imperial College London's Earth Science, Engineering, and Materials departments.
Three British geology students of Imperial College London have been fined in China for "illegal survey and map-making activities", according to local media. In addition to making maps, the students were researching fault lines and earthquake activity in Xinjiang — a tense Muslim province to the west of the country where anger against Chinese rule sparked deadly attacks in 2008. 

The students were gathering additional data in several regions, including Kashgar, the ancient Silk Road trading post, and an oasis city in the Xinjiang Uyghur Autonomous Region of the People's Republic of China. 

Under Dr. Jian Guo Liu, the students' supervisor at Imperial College, they also had been in the poor desert village of Keping, where in May local authorities burned the local mosque due to "unlawful religious activities". Of the three students, two of them, a PhD student aged 23, and a Master of Science student aged 22, went to Aksu Prefecture for their research.

In September, State Security Bureau officials had investigated the students at a hotel for several hours. Thereafter, their equipment, including GPS devices, survey results, and data, were seized. The Aksu Land and Resources Bureau officers claimed they had gathered "illegal data" from 6,000 points which was valuable for mineral prospecting and topographical research.

Korla, Xinjiang in the majestic Tian Shan mountain range. May 2007.
In the leadup to last year's summer Olympics in Beijing, China cracked down on map-making and data-collecting across the country. Despite having permission from the Earthquake Administration in the country, the students were fined a combined 20,000 yuan (2,940 dollars) but did not receive additional punishments. "The data they gathered would have been valuable in analysing mineral and topographic features of the areas," Xinjiang Daily said. They returned to the UK on October 2. 

According to The Procuratorial Daily, the Xinjiang prosecutors' office approved 1,295 arrests of individuals and indicted 1,154 suspects from January to November 2008. The indictments were based on suspicion of "endangering state security." In 2007, however, only 742 were arrested, while 619 of them were indicted for the same offense.