In his resignation statement, issued within an hour of the result of the vote being announced, Dr Owen said: "We (the SDP) are now deeply and predictably split."

Nearly 60% of the party, 25,897 members, voted for a full merger with the Liberal party.

Just over 42%, 19,228 members, voted for the second option, which was to create a closer framework with the Liberals, which would have preserved the SDP.

Dr Owen said: "The members have decided, as they have every right to do, to seek a merger with the Liberals against my advice.

Alternative to Thatcherism

"And in the circumstances I do not believe I should continue as their leader during the period of negotiations which will follow."

But Dr Owen does intend to remain in Parliament, as MP for Plymouth Devonport.

Leader of the Liberals David Steel welcomed the vote for a merger and said they would now be able to present "a clear and united alternative to Thatcherism and Socialism".

He said Dr Owen's resignation was "logical but not surprising".

David Owen was a founding member of the SDP when, alongside Shirley Williams, Roy Jenkins and Bill Rodgers, he defected from the Labour party in 1981.

The "gang of four", as they came to be known, cited major differences over European and defence policies and vowed to "change the mould of British politics."

Dr Owen, who has led the SDP since 1983, said he believed his party would continue to work with the Liberals but would not be drawn on his opinion as to whether the merger would be a success.

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