Margaret Thatcher was forced to tear up one of her most hard-hitting speeches, which would have gone beyond her controversial "The Enemy Within" remarks, in the wake of the Brighton bomb, newly released files reveal.

The former prime minister provoked outrage with her description of militant miners who resisted pit closures, which was delivered in a speech for the 1922 Committee in July 1984.

Her personal papers from that year, which contain the first handwritten draft of The Enemy Within speech, reveal that she had no plans to back down from making the provocative remarks.

A scribbled speech, released by the Margaret Thatcher Archive Trust, shows she planned to go further by launching a full frontal attack on the Labour Party at the Conservative Party conference in Brighton. Her plans were waylaid when an IRA bomb killed five people in October 1984.

The speech begins: "From the dark cloud falls an acid rain that eats into liberty."

It continues: "The Labour Party in its present form, infiltrated by extremists, riven by factions, still stands upon the stage as the alternative to the Conservative Party in governing Britain."

Chris Collins, from the Margaret Thatcher Foundation, said the words "would have eclipsed The Enemy Within speech, indeed it was intended to do that".

He added: "But tragic events overtook her and, instead of a moment which would have been remembered for decades, the speech ended up torn up and later taped back together."

The speech that was delivered contained fragments of its predecessor but with very few references to Labour.