I don't know much abotu physics or engineering but I know a little about law and architecture. Perhaps others know better than me.
Usually for architecture you need to be able to show a portfolio for admissions. Usually this is art but 3D design may be useful (I would check with admissions, though!). Some people use their portfolio from their Art A-level but I do know people who have made their portfolio outside their studies. Otherwise, it may be possible to do a foundation year (which is a more common occurrence in the arts).
For law, keep in mind that in the UK is is not necessary to study law as an undergrad in order to become a lawyer. I know people who studied music, art, politics etc and are successful, highly paid lawyers. There is a postgraduate law conversion path that lots of people take, however, it will take 1 more year to qualify as a lawyer on average. If you want to apply for law as a degree then you would likely need an essay-based subject for that (but I do not reccommend taking Law A-Level).
You may be able to pursue another A-Level/AS Level/EPQ outside of school. Some subjects (like Art History) are usually only offered in private schools, so there are non-profit organisations that to make them available for free to state school students (such as Art-History Link-Up). Would be worthwhile to research if any exist for A-Level subjects you like.