Excess water from water butts draining into main sewer

Can you have a soak away built. That is the best option. I’m sure on occasion people do run water into the main run. At least it would be kept clean. But really. Soak away.

You are not really supposed to put 'clean' rain water into the foul water system especially as you already have a soakaway. A couple of reasons, during storms and heavy rainfall, the foul water drains could get overwhelmed and cause a flood of the foul water. Next, the Water Companies will have to 'treat' the rain water when it has entered the foul water system and gone to the sewage treatment plant. As rain water, it doesnt need to be cleaned, such as surface water off roads are not cleaned but routed directly into rivers etc.. As you alreay have a soakaway, correctly fitted water butts should allow the rain water to go back into the rainwater pipes once the butts are full. Then the rain water will go into your soakaway and then into the water table and out to the sea/rivers etc... Sounds like your water butts are not fitted correctly as they are designed to do this.