A powerful panel of business leaders representing some of Britain’s biggest employers is embroiled in a row over assurances they are demanding from Theresa May about the terms of the UK’s departure from the EU.
Sky News has obtained a letter to the Prime Minister drafted this week by the Professional and Business Services Council (PBSC), the members of which include top executives from firms such as Arup, the engineering consultancy; Clifford Chance, the 'magic circle' law firm; Deloitte, the big four auditor; and McKinsey, the management consultants.
The draft expresses "great concern… that both the interim and final deal with the EU will not fully include the fundamental requirements to avoid sustained harm to our sectors and our clients, and thereby the wider economy".
Sources said that some members of the PBSC had expressed disquiet over the tone and content of the letter, and had sought in recent days to prevent it being sent to Mrs May.
One insider said the letter would not now be released in its current form, and that the PBSC's position would be reviewed in the wake of the European Council meeting later this month.
In their letter, the PBSC members, who also include bosses from Accenture, Allen & Overy, EY and Zygos, the headhunting firm, call for the PM to engineer a Brexit deal which includes mutual recognition of regulatory frameworks and bodies.
Professional services firms also needed an agreement with the EU which featured "mutual recognition of professional qualifications, products and operating licences; the ability of our providers to fly in-fly out to facilitate advice across the EU27 and trade across Europe; mutual recognition of judgments so deals across EU27 countries can proceed with legal certainty; and continued co-operation in areas that facilitate trade - such as data sharing".
It goes on to demand a deal "supported by the ability to recruit the best talent from overseas ensuring Britain continues as a global hub so our economy can grow and thrive; and we need certainty through any transition".
Failure to negotiate such a deal would "impair our ability to provide our services with the same range, depth and speed our clients around the world experience today, damaging their business and putting our sectors at a distinct competitive disadvantage", the PBSC warns.
The list of requests from the PBSC are far from unusual in containing sector-specific demands over the terms of the final Brexit deal.
Similar messages have been communicated by big employers and their representative bodies in industries such as financial services, automotive and pharmaceuticals, both in letters and roundtable meetings with the PM.
However, one member of the PBSC said the letter from the PBSC was "going to be sent to the wrong minister" and said that its tone was "patronising and passive-aggressive".
According to the PBSC, the sectors it encompasses employ 4.6m people in the UK "and contribute £188bn in gross value to Britain's bottom line".
Its members "combine to keep the wheels of the British economy turning" and "are worth more than the manufacturing, mining and extractive industries combined", the draft of the letter seen by Sky News claims.
The PBSC cites British professional services as "one of Britain's greatest exports".
"We are a key reason why people the world over come to do deals and resolve disputes in our country," its letter says.
"Our law is the gold standard, our accounting influential around the globe.
"Our architecture a visible symbol of our insight and innovation."
It concludes by acknowledging the EU's prioritisation of trade in goods in the Brexit talks, but insists that Mrs May seeks to "get the right deal on professional and other services given our relative strengths and current competitive position".
"The UK needs a deal that is good for Britain and one that works for the EU27.
"We look forward to hearing how you intend to secure the professional services success story in the years to come."
None of the PBSC members - which also include Jones Lang Lasalle, KPMG and Linklaters - contacted by Sky News would comment on the letter on Wednesday.