In a leaked memorandum, Jeremy Browne said French authorities were seeking "disruption".
"They are in favour of the hardest Brexit," he wrote.
"They are crystal clear about their underlying objective: the weakening of Britain, the ongoing degradation of the City of London."
Mr Browne a former Liberal Democrat minister and since 2015 the City's special representative to the EU, attended talks with various French authorities earlier this month.
The memorandum, which was leaked to the Mail on Sunday, summarised for ministers Mr Browne's impressions following those talks and others in Luxembourg, where he said the tone was more co-operative.
"The meeting with the French Central Bank was the worst I have had anywhere in the EU " he wrote.
He acknowledged that the French were possibly simply taking tough negotiating positions, the "bad cop" approach, but said that "nevertheless ... France sees Britain and the City of London as adversaries, not partners."
"Every country, not unreasonably, is alive to the opportunities that Brexit provides, but the French go further, making a virtue of rejecting a partnership model with Britain and seemingly happy to see outcomes detrimental to the City of London even if Paris is not the beneficiary."
Mr Browne said the mood in France was "more giddy and more assertive" since Emmanuel Macron was elected president in May and that "French representatives [were] currently crashing conspicuously around London, making heroic relocation promises."
Several European cities, including Frankfurt, Dublin and Brussels as well as Paris are vying to attract business that may shift out of London following the UK's departure from the EU.
Financial institutions are drawing up contingency plans to open new subsidiaries within the rest of the EU to ensure they can continue to do business-as-usual post-Brexit.
Mr Browne suggested that France's adversarial tone was jarring with other EU member states, aiming for a more conciliatory approach.
"There is plenty of anxiety elsewhere in the EU about the French throwing their weight around so aggressively, but their destructive impulses are not being confined, and other EU countries that want a friendly relationship with Britain and the City of London are being marginalised," he wrote.

Anna Egginton-Murray, who quit Lancashire Care NHS Foundation Trust in September, said there was nobody with the expertise to treat serious cases in the prisons she worked in.
She knew about 100 inmates with major problems who were "put on a list" of prisoners with "unmet needs".
The trust denied the list's existence and said severe cases were treated.
The Ministry of Justice declined to comment when contacted by the BBC saying this was not within its area of responsibility.
"It felt dangerous," said Ms Egginton-Murray, adding: "It felt unethical and it felt very sad."
Her claims were backed in written statements to BBC Inside Out North West from other staff who worked at the trust.
Cognitive behavioural therapist Ms Egginton-Murray treated prisoners with less serious conditions at Liverpool Prison and HMP Kennet, a prison for Category C inmates near Maghull.
She said there was nobody with the experience or expertise to deal with inmates when it became apparent they needed more specialised treatment.
Ms Egginton-Murray would discover a prisoner's deeper problems during her consultations and felt frustrated because there was nowhere she could refer them.
One inmate had post-traumatic stress disorder (PTSD) due to a childhood trauma and there was nothing she could do for him, she said.
She added: "There was a list of prisoners that were listed as 'unmet need' because there was no service there to meet their needs."
Ms Egginton-Murray, who left her post after 11 months, claimed there were almost 100 prisoners on that list, adding that her job "became very burdensome... very difficult."
"When you know there is nothing more you can do and you are faced with someone who is desperate for help and they're asking for help, it leaves you in a very difficult position."
The Lancashire Care NHS Foundation Trust said: "Prisoners with more severe mental health needs would not be put on a waiting list unless they are waiting for a secure in-patient bed outside of the prison.
"In the meantime their needs are managed within the prison."
Draft guidelines from the National Institute for Health and Care Excellence (Nice) state that people in prison "have the same rights of access to health care as the general population", but that "there is clear evidence that this is not the case".
France hopes that Brexit will weaken Britain and London's role as a financial centre, according to the City of London's envoy to the EU.
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Dozens of prison inmates with serious mental health problems are left untreated, a whistleblower has said.