Plastic consumer units burn, some are self extinguishing plastic so they stop burning if the heat source is removed, others just burn in an uncontrollable manner. If you don’t believe me try setting fire to an old plastic consumer unit or just a cable knockout blank from one. Even if the house or flat doesn’t burn down a consumer unit fire could result in the property being unfit to live in until it has been cleaned and redecorated, as well as the required electrical repairs being done. I have a plastic consumer unit in my garage, I am not particularly concerned about it, but if the case were to show any signs of heat damage I would switch it off and check it it immediately. @jeff williams you do indeed have an old and obsolete consumer unit that is no longer considered fit for purpose, the best advice is to replace it. See if you can get some other quotes, but you probably aren’t being conned.