The simple answer is,
Yes you will need a visa.
It doesn't matter if you were arrested and released, nor does it matter what the rules relating to spent convictions etc. are in your home country. Unfortunetaly, if you have ever been arrested whatever the circumstances then you cannot travel under the VWP.
From the US (London) Embassy website:
Travelers with arrests/conviction(s)
Under United States visa law people who have been arrested at anytime are not eligible to travel visa free under the Visa Waiver Program(VWP); they are required to apply for visas before traveling. If the arrest resulted in a conviction, the individual may require a special restricted visa in order to travel. The Rehabilitation of Offenders Act does not apply to United States visa law. Therefore, even travelers with a spent conviction are not eligible to travel visa free; they must apply for B-1 or B-2 visas. If they attempt to travel under the VWP, they may be refused entry into the United States.
Note. The grant of an ESTA does not confer eligibility to enter the US.
Authorization to travel under ESTA does not guarantee entry into the United States; that decision rests with the immigration official at the Port of Entry in the same way that travelers currently entering the U.S. under the Visa Waiver Program or with a visa are subject to inspection.
Incidentaly if you do need a B1/B2 visa you will need to move quickly. Because you have an "arrest" you will be required to take with you to the visa interview an ACPO police certificate (£35 - £75 depending how quickly you need it). The process is expensive and tedious.