Notwithstanding the "paper" issues of law/license/car spec etc. Trying to stop an extra 3/4 tonne load with a relatively light family saloon, will fundamentally alter the handling of the car in an emergency stop situation. Hopefully you'll live to regret not going braked.
About 20 years ago, I ran into the back of another car (Astra) whilst towing a 4 wheel braked boat trailer, we were in a traffic jam in October, it was raining & the roads were in that horrible, snotty, greasy autumnal state. I was doing 15mph & just gone into 2nd gear. The traffic stopped, I braked, the wheels on the trailer locked as did the car (both were examined after the accident by the police) we gracefully slid into the back of the Astra, the back window of the Astra blew out & went over the top of the Disco & landed in the boat. The rear of the Astra ceased to be, if there had been anyone on the back seat, they would probably have lost their legs. We closed the A1 for a couple of hours.
The police couldn't find fault with either trailer or vehicle & I wasn't prosecuted, it was "one of those things".
Our 2 year old was asleep in the back & never flinched throughout. The Astra was a write off, we had a cracked headlight on the Disco & drove home. The Policeman in charge at the scene commented on the damage to both vehicles & said that the Disco "wasn't very car friendly" I looked at the damaged Astra & asked him which vehicle would he rather have been in
So my point?
When it's hitting the fan, you need all the help you can get & you'll be glad of it, regardless of what the law says you can get away with.
I'll get off my soap box now