Many thanks for your patience. First of all, the law does not really offer compensation for 'what could have happened'. Therefore, you would not get anything for potential risks or injuries, a court would only look at actual thongs that have happened, actual injuries or costs.
In terms of the general laws on this, when a person enters into a contract for work and materials, where the main focus is labour and skill, the Consumer Rights Act 2015 says that the work must be carried out with reasonable care and skill (to the same standard as any reasonably competent person in that trade or profession)
If there are problems with any of the above, the customer will have certain rights and in the case of substandard work - the trader should either redo the parts of the work which are inadequate or perform the whole service again at no extra cost to the customer. This must be done within a reasonable time and without causing significant inconvenience. If this is not possible, you can claim a price reduction, based on the severity of the issues. If they simply refuse to resolve the issues, you can consider getting someone else to rectify the issues and either deduct these costs from the total owed to the original trader, or pursue them for any extra costs that have been incurred.
I would say that due to what happened you will likely have grounds to refuse to work with them any further as their initial work was negligent. So you may not have to pay for the work carried out s far, but cannot expect them to fix the car for free either. However, if any damage was caused to your car they would be expected to either repair it or compensate you for the costs of getting it done elsewhere.
Does this answer your query?