BGC Partners, the interdealer broker, set aside more than £40 million for a secret plot to poach around 50 staff from arch-rival Tullett Prebon, the High Court heard today.

The plan, through which BGC hoped to lure its rivals “crown jewels”, was arranged via mobile phones which were deliberately thrown away to cover the conspirators tracks, it was alleged.

Opening a court case in which Tullett is suing BGC and several of its own former staff, Daniel Oudkerk, representing Tullett, said: “At the heart of this case is an unlawful conspiracy to poach [Tullett’s] brokers.”

Mr Oudkerk said the plan, in which over 50 Tullett brokers were approached, was masterminded by Tullett’s former chief operating officer, Tony Verrier, who joined BGC this year. He claimed Mr Verrier conspired with Shaun Lynn, BGC’s president, to hire Tullett desk heads who would then be used as “recruiting sergeants” to bring the rest of their team.

One desk head, James Bowditch, whose team traded sterling derivatives, was offered a £1.1 million sign-on bonus on top of a £400,000 salary and £400,000 guaranteed year-end bonus. Another Tullett desk head, James Hall, was offered a £750,000 sign-on bonus.

Mr Oudkerk said: “It is perfectly clear that sums of this scale were intended to incentivise these desk heads to recruit their desks to BGC.”

The plan, run under codenames including “Project Wire” and “Project Phoenix, cost BGC “well in excess of £40 million,” Mr Oudkerk said.

Once the Tullettt brokers had been convinced to defect to BGC, Mr Verrier co-ordinated their mass resignation, the court heard.

He also hired a leading employment lawyer to concoct a “sham” that would excuse the brokers from contractual obligations preventing them from joining BGC immediately, the court heard.

Many of the defecting brokers had signed contracts barring them from joining a rival for 120 days after they resigned.

Mr Oudkerk said that Mr Verrier, with the help of John Marshall, a partner at law firm RJW, sought to invalidate these contractual blocks

In order to leave and join BGC immediately the brokers “needed a veneer,” Mr Oudkerk said, so “Mr Marshall and BGC put together a series of sham constructive dismissal claims [against Tullett].

This included Mr Verrier encouraging the defecting Tullett brokers to write to Tullett using the set text of a letter drafted by Mr Marshall and BGC.

The letter allowed each broker to claim they had become “stressed by the aggressive strong arm-tactics being used by Tullettt to try to convince me not to move to BGC”, Mr Oudkerk said.

The letters were part of Mr Verrier’s “early exit strategy” for the brokers, the court heard.

The court heard that the conspiracy, which it is alleged began in August 2008, involved 45,000 mobile phone calls and text messages.

Mr Oudkerk said the court could not see records of the text messages because they are stored only on individual phones.

He told the court that after Tullett became aware of the alleged conspiracy, it issued legal proceedings that would eventually require the senior brokers to surrender their mobile phones.

Mr Oudkerk said Mr Hall “lost his phone within hours” of being asked to produce it and Mr Bowditch “lost” his phone “the day after” he received a similar request.

In a 12-month period, Mr Verrier “lost 7 Blackberries”, the court heard.

“We don’t shrink from saying in this case that mobile phones have been used to further the conspiracy and have been disposed of to conceal the conspiracy,” Mr Oudkerk said.

BGC Partners said: “We continue to expand geographically, enter new product areas and increase its broker headcount.

"This, along with the strength of our management team and industry leading technology platform, means that BGC Partners is consistently sought out by some of the marketplace's most experienced brokers, and continues to attract top talent. As such we fully contest these allegations.”

A spokesman for Mr Verrier said he denies all allegations. Mr Hall and Mr Bowditch could not be reached for comment.

One of the legal principles in question is where the dividing line lies between an open expression of willingness to hire rival staff and interference, which amounts to breaching the contracts between them and their current employer.

The case continues.

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