Tony Blair has agreed to advise the Egyptian president, Abdel Fattah el-Sisi, who came to power in a military coup last year, as part of a programme funded by the United Arab Emirates that has promised to deliver huge "business opportunities" to those involved, the Guardian has learned.

The former prime minister, now Middle East peace envoy, who supported the coup against Egypt's elected president Mohamed Morsi, is to give Sisi advice on "economic reform" in collaboration with a UAE-financed taskforce in Cairo – a decision criticised by one former ally.

The UAE taskforce is being run by the management consultancy Strategy&, formerly Booz and Co, now part of PricewaterhouseCoopers, to attract investment into Egypt's crisis-ridden economy at a forthcoming Egypt donors' conference sponsored by the oil-rich UAE, Kuwait and Saudi Arabia.

Blair's decision to become involved in Gulf-financed support of the Sisi regime, which is estimated to have killed more than 2,500 protesters and jailed more than 20,000 over the past year, has been attacked.

A former close political associate argued that the ex-prime minister's role in advising the Egyptian regime would cause "terrible damage to him, the rest of us and New Labour's legacy".

Blair's spokeswoman told the Guardian that his backing for "Egypt accessing support in the international community" was not being done "for any personal gain whatsoever". He would make no money out of Egypt and neither would any of his organisations. "He is giving advice, he will have meetings, that's all," she said adding that he "is not a formal adviser".

Blair believed that the Sisi government in Egypt "should be supported in its reform agenda and he will help in any way he can, but not as part of a team". However, he regarded Strategy&'s Egyptian work as important.

It is understood that correspondence from Blair's office in support of Egypt's economic reform and investment programme suggests lucrative "business opportunities", in Egypt and the Gulf, are expected for those taking part. Blair's spokeswoman said: "We are not looking at any business opportunities in Egypt."

The former political associate said a bargain had been struck. "Tony Blair has become Sisi's éminence grise and is working on the economic plan that the UAE is paying for. For him, it combines both an existential battle against Islamism and mouth-watering business opportunities in return for the kind of persuasive advocacy he provided George Bush over Iraq."

"It's a very lucrative business model," the associate added, "but he shouldn't be doing it. He's putting himself in hock to a regime that imprisons journalists. He's digging a deeper and deeper hole for himself and everyone associated with him."

Alastair Campbell, Blair's former press secretary who resigned in 2003 over the Iraq war "dodgy dossier" scandal, is also advising the Sisi government on its public image and being paid for it – though he refused to say if he had been working with Strategy&.

Like the former prime minister, Campbell visited Cairo earlier this year as part of the Gulf-funded programme to bolster the regime. Darren Murphy, who worked for Blair in Downing Street when he was prime minister, has also been working on the programme. Blair's spokeswoman said the former prime minister would "introduce people" in the Egyptian capital if that was "helpful". Some observers argue that the UAE-funded Egyptian taskforce in Cairo now forms a shadow government within the government. Since standing down as prime minister in 2007, Blair and his companies have been awarded a string of multimillion consultancy contracts with private corporations, dictatorships and repressive regimes, including Kazakhstan, Kuwait, the UAE and Colombia. They include a contract worth more than £1m a year to advise the UAE's Abu Dhabi sovereign wealth fund Mubadala.

But his involvement with the Egyptian dictatorship is likely to be his most controversial, both because of its overthrow of a democratic government and the scale of bloodletting it has unleashed – and because of Egypt's central role in the Middle East where he has been the peace envoy of the Quartet of the US, EU, UN and Russia since 2007.

Last week a group of former British ambassadors and political figures joined a campaign to call for Blair to be sacked as Middle East envoy, citing his "negligible" achievements in the role, his defence of military intervention in Iraq and Syria and the "blurring the lines between his public position as envoy" and his private business dealings in the Middle East.

Chris Doyle, of the Council for Arab-British Understanding, said his business interests and peace envoy roles were "incompatible and create a huge conflict of interest".

Sisi seized power last July as army commander-in-chief and was confirmed as president this month with 96% of the vote in a dictatorial-style election after Morsi's Muslim Brotherhood had been banned as a terrorist organisation.

Blair congratulated him on winning the support of the people and said he deserved the support of the whole international community. But he criticised the recent jailing of al-Jazeera journalists as unjustified. In April, Blair singled out the Muslim Brotherhood and other Islamists as the enemy that the west and east should unite against and hailed Morsi's overthrow as "the absolutely necessary rescue of a nation".

That is also the view of the autocratic governments in the UAE and Saudi Arabia that are now funding the Sisi regime in Egypt and see themselves as the spearhead of a life-and-death regional struggle against political Islam.

Pressure from the UAE and Saudi Arabia led David Cameron to launch an inquiry into the Muslim Brotherhood and its alleged links to extremism earlier this year. Blair has also commissioned his own report into the Brotherhood, reportedly on behalf of the UAE.

Aides to Blair confirmed last week that he is considering opening an office in Abu Dhabi, capital of the UAE – where he is reported to be especially close to the crown prince, Sheikh Mohammed bin Zayed al-Nahyan – to strengthen his links with the Gulf autocracies.

His business dealings and consultancies are obscured by a network of companies and partnerships that allow him to avoid publishing full accounts. But his earnings were reported last year to be more than £20m a year.

• Since the publication of this story, Tony Blair's office has issued this statement.