Colonel Collins, who will leave the Army in the summer, became the most famous soldier in Iraq when the speech he made addresssing his troops as they waited on the startline ahead of crossing from Kuwait into battle was reported on around the world.
News of Collins' resignation came at the weekend when the commander of the 1st Battalion The Royal Irish Regiment tendered his resignation from the Army after 22 years of service.
It is expected he could earn as much as £150,000 as a PR consultant in the private sector, almost three times his military salary. Last year he won a top award at the PR Week Awards for his speech in which he told his men: "We are going in to liberate, not to conquer. We are entering Iraq to free people. Show them respect. If you are ferocious in battle, remember to be magnanimous in victory."
Collins' speech won widespread praise -- President George Bush is reported to have framed it -- and made him a focus of much attention.
The attention is believed to have contributed to unfounded accusations from an American reservist, later sacked, that he had mistreated Iraqi civilians and PoWs. The Ministry of Defence went on to clear Colonel Collins but he is thought to have been unhappy with the lack of support he received from senior Army officers.
His departure is reported to stem from disillusionment following the investigation, during which he spent several months on gardening leave while the Royal Military Police investigated the claims. He went on to serve in Bosnia after leaving Iraq.
Weekend reports also said Colonel Collins had resigned because crippling government cuts were ruining the Army.
His wife told the Sunday Telegraph: "Tim is no longer convinced that the Army reflects the country with the fourth-largest economy in the world. He fears it is becoming a cottage industry."
His departure from the Army is a bow for the top brass because Colonel Collins was destined for the top and was being talked about as the next Director Special Forces, which would have put him in charge of the SAS and Special Boat Service.
The MoD refused to comment on his departure.
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