Three other senior executives who resigned on Monday were named as co-conspirators in the writ. They are Jeremy Sinclair, who took over as acting chairman following Mr Saatchi's departure and was the company's chief creative director; Bill Muirhead, who was head of North American operations, and David Kershaw, who was chief executive of the European business.
Sir Tim Bell, Maurice Saatchi's spokesman, said: "This is not unexpected. We will be issuing counter-writs. We always anticipated a legal battle."
Wendy Smyth, finance director, said the company still wished to discusss with Charles Saatchi the removal of 15 filing cabinets from the head offices on 3 January.
Asked whether the company might ask him to resign, she said: "I can't comment on his position at this moment, but I might be able to tomorrow. He's in a rather difficult position, and he hasn't been in his office since the new year." Charles Saatchi is actively involved on only the account for Gallaher, the giant cigarette group.
On the writ, a company spokesman said: "It claims damages against all four of them for a conspiracy to injure the business of the group and against Maurice Saatchi for soliciting the other three.
"It also seeks to prevent Jeremy Sinclair, David Kershaw and Bill Muirhead from joining a competing business, soliciting or working for clients of Saatchi & Saatchi in a competing business and damages for breach of contract."
A spokesman for Messrs Kerhsaw, Muirhead, and Sinclair had no comment to make until they had taken legal advice. All three had non-competitive clauses of at least a year written into their contracts.
Saatchi & Saatchi is calling for a hearing in the Chancery division of the High Court, at which it will seek restraining injunctions. It also wants the hearing to be held before the end of the month and before a judge in open court.
The spokesman added: "The most contentious issue is the allegation of conspiracy. To reduce the risk of counter-claim for defamation, we are just restricted to making comment on what is in the writ."
Saatchi's share price yesterday continued to suffer. The middle market price fell 11p to a four-year low of 96p in early dealings, and closed at 97p.
Investors ditched shares at an alarming rate in response to the loss on Wednesday night of the high-profile accounts of British Airways and Mirror Group. More than 19 million were traded, nearly 9 per cent of the total number of shares in issue.
Some investors sold shares at prices as low as 93p, a level they last traded at in 1978 .
Several media analysts said investors were panicking unnecessarily.
Outlook, page 29
Timetable of turmoil at Saatchi December 94 Shareholders, led by David Herro, attack £5m share option plan for Maurice Saatchi.
16 Dec Maurice resigns as chairman, and considers offer to become chairman of advertising worldwide. Leading clients voice concern over developments.
18 Dec Maurice given 3 January deadline to accept job offer.
30 Dec Maurice offered £100,000 pay rise to stay.
3 Jan 1995 Maurice quits group entirely, and removes 15 filing cabinets. from head office.
5 Jan Company discovers files are missing. Threatens legal action.
9 Jan Three key directors, Jeremy Sinclair, David Kershaw, and Bill Muirhead, resign. Shares drop 16p to 124p.
10 Jan Stock Exchange launches insider dealing inquiry.
11 Jan Moray MacLennan, Nick Hurrell, Simon Dicketts, and James Lowther resign. Maurice starts new agency.