UK Serious Fraud Office officials have visited Tanzania, as part of a probe into the purchase of an air traffic control system five years ago.
Tanzania's main airport benefited from the deal
Tanzanian President Jakaya Kikwete said in the UK he would give no more details to avoid influencing the investigation.
The UK Guardian newspaper reported that British defence company, BAE Systems, allegedly paid a Tanzanian middleman a commission of $12m to win the order.
BAE says it is cooperating fully with the investigation.
At the time, the serving UK International Development Secretary Clare Short criticised the sale of such an expensive system.
Neither the BAE nor the SFO are commenting on recent developments.
BAE has strongly denied operating a secret slush fund to sweeten deals.
The SFO recently decided to drop a long-running BAE corruption probe into a huge arms deal with Saudi Arabia.
Reports said the Saudis had threatened to pull out of a new BAE deal unless the probe was brought to an end.
Opposition politicians accused the government of putting cash before principle.