Complex sentence: Only the intervention of Major-General Urquhart who had just been freed from where he had been trapped stopped the 11 Para assault, Urquhart having recognised the futility of the battle was not prepared to reinforce failure.
Split into simpler sentences: Only the intervention of Major-General Urquhart, just freed from where he had been trapped, stopped the 11 Para assault. Having recognised the futility of the battle Urquhart was not prepared to reinforce failure.