The first thing I would stress is that you have not done poorly in your A-levels - they are still great grades.
Unfortunately, firms will only consider your top three A-level grades for the UCAS calculation (excluding subjects like General Studies/Critical Thinking A-levels) and also when they are sat in the same year.
In 2017, CC removed all academic requirements from their roles -
How we hire (cliffordchance.com) so I don't think your ABC grades will be an issue for them
Freshfields hasn't had an A-level requirement for at least 9 years now and their website still states they do not have a minimum A-level requirement on their website, so again, I don't think there are any issues in applying for them.
It may be an issue for other firms that do ask for ABB (or above) grades though