Nimrod surveillance aircraft flying over Helmand province recently picked up voices lapsing from local languages into English with Midlands and Yorkshire accents, according to reports.
Inayat Bunglawala, assistant secretary-general of the Muslim Council of Britain, said he was aware that some British Muslims travelled to Afghanistan to fight when hostilities began in 2001.
He had heard of no cases since then, but accepted it was "not beyond the bounds of possibility", given that the conflict had "dragged on with still no end in sight".
Linguists on board the Nimrods from 51 Squadron, normally based at RAF Waddington in Lincolnshire, detected the British voices while listening in on Taliban radio traffic, according to The Sun.
An unnamed RAF source told the newspaper: "The missions specialists could easily jam the Taliban transmissions - but the RAF believes listening in to their plans is much more productive.
"It was quite startling to hear English being spoken with clear Bradford and West Brom accents.
"They reverted to English when they couldn't remember the Afghan Persian or Pashto - the two local languages - for certain words."
The Ministry of Defence (MoD) would not confirm the report, but it said the Nimrods had "highly sophisticated and sensitive" reconnaissance equipment.
Mr Bunglawala said: "I do know when the initial bombing was occurring in late 2001, there was a lot of sympathy for the Afghan people, who had endured so much.
"I am surprised if people are going now. I wasn't surprised then, but I am surprised now.
"That's the effect of the conflict having dragged on. We were told it would all be over in a few weeks, but the conflict has dragged on with still no end in sight."
He urged British Muslims opposed to the war in Afghanistan to protest peacefully using the democratic means available in the UK.
He added: "I don't think it can be denied that our actions overseas have contributed to some British Muslims being radicalised.
"Our advice to youngsters is to campaign within the democratic framework here.
"Going to fight British soldiers in Afghanistan leaves them open to accusations, quite rightly, that they are betraying their own country."
The MoD said in a statement: "The Nimrod R1 operated by No 51 Squadron has a highly sophisticated and sensitive suite of systems used for reconnaissance and gathering electronic intelligence.
"However, due to operational security, we are unable to discuss its operational capability."
Source: Metro (English)