The Foreign Office has warned against all but essential travel to Sri Lanka following the Easter Sunday bombings.
Foreign Secretary Jeremy Hunt said: “Our hope is that it will be possible to change this when the current security operation has concluded.
“My first priority will always be the security of British citizens living and travelling abroad.”
It comes as the family of Bill Harrop, from Manchester, paid tribute to the retired firefighter, who died in an explosion at the Cinnamon Grand Hotel alongside his wife, Sally Bradley, a GP.
His sons, Gavin and Miles, said in a statement: “Our beloved father Bill Harrop was a devoted father, the best anyone could wish for.
“On his retirement Bill moved to Australia with Sally to embark on new adventures, which have been so cruelly ended.
“His happiest times were spent with his family, sharing good times as we explored the world.”
Nine bombers co-ordinated blasts targeting churches and hotels in the country, killing 253 people – including eight Britons – and injuring hundreds.
Sir Lankan authorities on Thursday lowered the death toll from 359 people, citing chaotic bombing scenes for the discrepancy.
One suicide bomber reportedly educated in the UK was radicalised after leaving Britain, his sister has said.
Abdul Lathief Jameel Mohamed is understood to have studied in the south-east of England between 2006 and 2007, later completing a postgraduate course in Australia.
His sister Samsul Hidaya told MailOnline: “My brother became deeply, deeply religious while he was in Australia, he came back to Sri Lanka a different man.
“He had a long beard and had lost his sense of humour.”
She told the news site he ended up “really angry and totally crazy”, and admonished male relatives who shaved their beards.
Mohamed is reported to have studied aerospace engineering at Kingston University in south-west London, but the university on Thursday said it could not confirm this.
The identity of Mohamed was first reported by Sky News, which said he was in the UK between January 2006 and September 2007, before returning to the UK in 2008 for a period.
Two of the bombers were the sons of a wealthy spice trader, according to media reports.
The father of the men was reportedly arrested on Thursday on suspicion of aiding his sons.
Many of the attackers came from well-educated, middle-class families, and had been part of a pair of little-known extremist Muslim groups, Sri Lanka’s junior defence minister Ruwan Wijewardene told reporters.
Police in the Sri Lankan capital Colombo have detained 58 people in connection with the bombings, claimed by the Islamic State group.
“Terrorists are very likely to try to carry out attacks in Sri Lanka. Attacks could be indiscriminate, including in places visited by foreigners,” updated Foreign Office guidance said on Thursday.
Among the British victims were Anita Nicholson, her son Alex, 14, and daughter Annabel, 11, who died when one of seven suicide bombers struck as they ate breakfast at the Shangri-La hotel in Colombo.
Londoner Matthew Linsey’s daughter Amelie, 15, and son Daniel, 19, were killed in the same blast on the final day of their holiday.
IT specialist Lorraine Campbell, 55, was also in the Cinnamon Grand on a work trip when she was killed.
Her husband Neil Evans said: “Lorraine was a real tour de force. She epitomised the qualities she lived by, and was a conduit for bringing people together to both make things happen, and make them better.
“I’ve lost my best friend in the world for all the adventures we shared and planned for the future.”
Juno Srivastava, a student at Middlesex University Dubai campus, also died in the blasts, while a locally employed British Council worker was said to be in hospital with his wife, both seriously injured.
Specialist officers from the Metropolitan Police’s Counter Terrorism Command have been sent to the country to support the bereaved and Scotland Yard has asked for images or video taken during the attacks.