The head of MI6 had a secret Cold War slush fund pay for black ops to destabilise the Middle East and North Africa, declassified documents reveal.

Sir Stewart Menzies used the secret account to bankroll covert operations and plans to launch assassinations and topple regimes deemed troublesome to the British.

The account - which had £1.4m which roughly converts in £39m in today's money - was kept hidden from Government officials and even the MI6's own finance director.

Documents unearthed in the depths of the National Archive warned the cash would have allowed the powerful spy chief - known as 'C' - to carry out his own unofficial foreign policy.

Sir Stewart Menzies, head of MI6 after the Second World War, pictured with his bride Pamela. Sir Stewart had a secret fund which he used to pay for black ops against countries including Egypt, Syria Lebanon and the Sudan

It states: 'The use of such unofficial reserves by "C" without the prior consent of the Foreign Office, could enable him to carry out policies other than those approved by the Foreign Office and without their knowledge.

'Clearly this was unlikely to happen, but it would be wrong not to preserve against it.'

The top secret fund was set up in the wake of World War Two, and Sir Stewart said the cash was keep in case he needed to bribe foreign officials or protect the secret service from Budget cuts.

Where the money came from remains shrouded in mystery experts have speculated the US may helped bankroll it.

The files, revealed to the BBC, refer to operations Scant, Scream, Sawdust, and Straggle - secret missions against Sudan, Oman, Lebanon, Syria and Egypt.

Some £200,000 was spent on Operation Sawdust - a shadowy mission thought to have been launched against President Nasser, Egypt's powerful nationalist leader.

While most of these operations were propaganda efforts to try to turn the tide of public opinion against leaders who were a thorn in the side of the British establishment, others were more sinister.

Egyptian President Gamal Abdel Nasser (pictured right at the start of talks on Suez in 1956, with Egyptian foreign minister Mahmoud Fazwi in the centre and Australian PM Robert Menzies left). President Nasser is understood to be one of the Middle Eastern leaders the slush fund was used to launch operations against

These included plans to assassinate senior officials in Syria and elsewhere in a bid to topple the regime, although these were not enacted.

And many of these operations were running after Britain's humiliating defeat trying to recapture Suez Canal in 1956 - showing the UK was still trying to cling on to cling on to its global role.

Stephen Dorril, an MI6 expert who reviewed the files, said: 'If you add all these up, what you discover is a big increase in the number of special operations post-Suez.

'There had been an idea that Suez dealt a major blow to Britain and MI6 but actually they came back.'

Sir Stewart came clean to officials about the money in 1952 when he was getting ready to step down from MI6, and said the cash was set aside for bribes and in case of cuts to the service.

According to the documents he said: 'He thought it right to have a large sum to meet such contingencies as (a) a very large inducement to some person in an absolutely key position, or (b) the Vote for the Service being drastically cut in some political emergency in a way which would make it impossible to carry on the Service in the way it was necessary.'

The full story of the fund will be told in 'MI6's Secret Slush Fund' on BBC Radio 4 tonight at 8pm.