Unfair dangerous driving charge

Guy was driving at 45 mph in outside lane dual carriageway. He increased sped and suddenly let of the accelerator (no obstructions ahead) which caused my car to be quite close to his. He then slammed on the breaks causing me to have to slam on my breaks which caused me to slightly swerve into the inside lane. In pure shock I flashed my lights at him. Police pull me over and before asking for explanation say they're taking me and the other driver to court for dangerous driving. I believe that the officer believed before getting my statement that I had been tailgating and intimating the other driver. He cautioned me and took my statement where I explained what the other driver did. he had then calmed down and was saying my offence was tailgating but because he had already spoken to his Sargent he would have to prosecute for dangerous driving.
Police officer said he realised I had no points in my 10 years of driving and don't drive a fast car but that I have to accept that the other guy is a bad driver.
How can he say this but still charge me with dangerous driving where I risk losing my licence etc. He said it may be reduced to careless driving or no charge.
So because an officer was angry and what he believed he saw and what actually happened is different Im now in this situation and worried sick. I accept that due to the other drivers actions I was closer than I should have been but I'm definitely not a dangerous driver!! (Police also have it on video)
Advice please? What should I do now?