A former Tory peer who was jailed over the parliamentary expenses scandal has won £3,500 damages from Essex Police.
Lord Hanningfield, 72, sued for compensation over events in September 2011 - days after his release from prison on a tag after serving nine weeks of a nine-month sentence for false accounting.
The police, who denied that his arrest, detention and the search of his home near Chelmsford were unlawful, were conducting an investigation into expenses from when the peer was leader of Essex County Council.
It was later discontinued without any charges being brought.
Lord Hanningfield, who was not at London's High Court for today's ruling, claimed officers did not have reasonable grounds for believing that his arrest was "necessary" within the terms of the Police and Criminal Evidence Act 1984.
Mr Justice Eady concluded that the requirement of "necessity" as laid down by Parliament had not, on any realistic interpretation of the word, been met.
The judge said that, in the light of his findings, the amount of damages had been agreed.
Giving evidence, Lord Hanningfield said he was surprised and upset when he heard about the Essex investigation and thought the allegation against him was "ridiculous".
"I did not take it that seriously because I knew there was nothing in it."
He said recent events had left him on the verge of a nervous breakdown and in need of anti-depressants.
"It's been like a tsunami overwhelming me."
On the morning of the raid, he was woken by the barking of his Pyrenean mountain dog, which had slept on the floor of his bedroom since the onset of his nervous problems.
"When I wake up, having been in prison, I still sometimes have a job realising exactly where I am. I looked out of the window and saw several cars and a policeman with what I assumed was a warrant.
"I had been out of prison a few days, I was on a tag, I was still in a state of trauma and shock."
Lord Hanningfield said he did not invite the police in but did not stop them: "I just let them in."
He felt he was being hurried and was worried about keeping a medical appointment that day and leaving the dog.
After today's decision, Lord Hanningfield said: "I am delighted with the outcome.
"This case was never about winning money but was to prove a point that the officers were wrong to simply assume I would not co-operate with them when I co-operated fully with the previous inquiry.
"I hope that further council tax is not wasted by them taking this matter further."
Mark Spragg, his solicitor from Keystone Law, said: "This was an important case. It reminds the police that arrests should never be made without first considering whether there is a viable alternative to depriving someone of their liberty and invading their home, which there plainly was in this case.
"Lord Hanningfield is not above the law but neither does he fall beneath it because of his conviction. It can only be hoped that Essex Police can now accept the decision of the court in this matter and save Essex further expense."
Lord Hanningfield was arrested at 6.45am and, after being allowed to wash, dress and eat, taken to Braintree police station where he was held until mid-afternoon.
The police argued that, on the information known to the arresting officer, he had "more than reasonable" grounds to believe the summary arrest was necessary and, if that was lawful, it followed that the detention and search were as well.
In his ruling, the judge said that summary arrest was never going to have any impact on the prompt and effective investigation of Lord Hanningfield's council expenses.
"It is not for a judge to second-guess the operational decisions of experienced police officers, but in the circumstances of this case I cannot accept that there was any rational basis for rejecting alternative procedures, such as those adopted successfully by the Metropolitan Police.
"There were simply no solid grounds to suppose that he would suddenly start to hide or destroy evidence, or that he would make inappropriate contacts. There was only the theoretical possibility that he might do so.
"I can, therefore, see no justification for by-passing all the usual statutory safeguards involved in obtaining a warrant."
Later, Essex Police said: "Essex Police is disappointed with today's judgment and are considering the merits of appealing the decision.
"We note that the court accepted that officers had acted in good faith and that they had honestly believed the arrest was necessary. The decision to arrest is never taken lightly and we recognise the right of individuals to challenge such decisions before the courts."