The Conservative Party's proposal to fold the Serious Fraud Office (SFO) into the National Crime Agency (NCA) has been questioned by City partners, amid concerns that recent progress made by the organisation could be squandered by an overhaul of the current regime.

The party's election manifesto, released yesterday (18 May), describes the proposed move as an attempt to "strengthen Britain's response to white-collar crime" by "improving intelligence sharing and bolstering the investigation of serious fraud, money laundering and financial crime".

The proposal to merge the SFO into the NCA has been mooted before, with the Home Office – under then Home Secretary Theresa May – handing the organisation a 'stay of execution' in 2011, after floating plans to separate its prosecution division from its investigatory function.

Yesterday's manifesto announcement has been met with a broadly negative response from City white-collar crime partners, given the progress the SFO has made in recent years in securing high profile deferred prosecution agreements (DPAs) under new powers granted to it in 2014.

White & Case white-collar partner Jonathan Pickworth said: "This has long been an obsession of Theresa May's. The SFO has made real progress with its assault on privilege and securing significant resolutions in a number of recent cases, including the Rolls-Royce and Tesco DPAs. Just as the SFO is making real progress, the rug is pulled from underneath it."

The Rolls-Royce DPA, secured in January this year, saw the company agree a settlement of almost £500m with the SFO following a four-year bribery and corruption investigation. This was followed by the DPA struck with Tesco, in which the retail giant agreed to pay a £129m fine to avoid prosecution for overstating its profits in 2014.

Pickworth adds: "The SFO model, with its combined investigators and prosecutors in one agency, is a good one. It does a difficult and sometimes impossible task. It has become more focused and nimble. What is the sense in rolling a 30-year old agency with all its revenue generation, prosecutorial success and extensive experience into an unproven sprawling entity in its infancy, which has yet to prove itself?"

The NCA was established in 2013 as a successor to the Serious Organised Crime Agency, taking on responsibility for tackling money laundering, cybercrime and other offences such as human trafficking.

Latham & Watkins partner Stuart Alford QC, who focuses on economic crime and regulatory matters, commented: "The SFO has been securing unprecedented levels of success in DPAs, judicial review decisions and at trial. All participants in the UK markets benefit from having a strong, principled and well-run fraud office; it must be hoped that the NCA can deliver the same very high standards. The SFO has never been better regarded overseas and an important part of the global efforts to tackle financial crime is at risk."

Pinsent Masons corporate crime partner Barry Vitou added: "The most important thing is that, if this goes through, the people inside the SFO know what is actually going to happen. The transfer of the SFO's remit to the NCA will need to be monitored closely – and progress regularly reviewed. Transparency surrounding the process and what impact the NCA has on serious fraud will be essential Merging the SFO into the NCA should not result in a diminished law enforcement capability when it comes to investigating and prosecuting serious or complex fraud."

An SFO spokesperson said: "This is a political pledge and we cannot comment. The organisation of law enforcement is a matter for ministers."