BAT said it is conducting its own investigation through external advisers and had been co-operating with the SFO, added it would continue to do so during the SFO’s investigation.

‘The SFO confirms it is investigating suspicions of corruption in the conduct of business by BAT p.l.c, its subsidiaries and associated persons,’ the SFO said in a statement.

The allegations were first made in a BBC Panorama programme aired in 2015. The programme showed documents appearing to detail payments made to politicians and civil servants in East Africa, including Kenya, with the aim of influencing laws affecting the use of tobacco.

Following the SFO’s announcement, BAT said in a statement: ‘As previously announced, we are investigating, through external legal advisers, allegations of misconduct.

‘We have been co-operating with the SFO and BAT has been informed that the SFO has now opened a formal investigation. BAT intends to co-operate with that investigation.’

The Conservative party included a pledge to incorporate the SFO into the National Crime Agency in its manifesto, but following its failure to secure a majority in the general election, those plans have been shelved.

Theresa May’s attempts to incorporate the SFO into the National Crime Agency were foiled by her cabinet colleagues while she was home secretary.

Already this year, the SFO has fined engine maker Rolls-Royce £500m for bribery and Tesco £130m for misstating its accounts.

The SFO's announcement can be seen here.