Strictly speaking, if you want to become a solicitor, you would only need to complete the SQE which doesn't require your undergrad to be in any specific subject (not even law). However, the specific law firm that you want to apply to might be picky about this and insist on you having a PGDL.
To become a barrister, you would need a PGDL (unless you want to spend at least another 2 years doing an undergrad law degree). There are accelerated law degrees that you can do if you previously did an undergrad in another subject so you would only end up spending 2 years instead of 3 for the degree (you would start from Year 2 as opposed to Year 1). However, I consider this unnecessary if your aim is to just get into law.
No, not all unis offer PGDL for some reason. The list of PGDL courses are in the following link:
https://careerinlaw.net/uk/law-conversion-course-pgdl/pgdl-course-comparisonExamples of accelerated law degrees are the following:
https://www.law.ac.uk/study/undergraduate/law/accelerated-llb-hons-law/https://www.herts.ac.uk/courses/undergraduate/bachelor-of-laws-llb-hons-acceleratedhttps://www.southampton.ac.uk/courses/law-accelerated-programme-degree-llbThere are also specific degrees that are considered qualified law degrees (if they aren't, they're not considered adequate for entry into law and you would end up doing a PGDL on top). See the following:
https://www.sra.org.uk/become-solicitor/legal-practice-course-route/qualifying-law-degree-common-professional-examination/qualifying-law-degree-providers/Whilst accelerated law degrees don't seem to be included on the list, I think it's safe to say that if you want to do a law degree from a uni that's listed in the above link, there's a strong chance that the accelerated degree should also be qualified as well (especially if you end up with LLB after your name). You can check with undergrad admissions to be sure.
Do note, since you are thinking of doing a PGDL, you would likely need to fund it yourself - it's not a course that Student Finance pays for (see:
https://www.allaboutlaw.co.uk/school-leaver-law-careers/university-funding/funding-the-law-conversion-course#:~:text=The%20PGDL%20is%20not%20eligible,for%20a%20Postgraduate%20Master's%20Loan.). The typical tuition fees range from £6k to £12k. See:
https://www.thelawyerportal.com/study-law/gdl/gdl-costs-gdl-funding/Likewise, law isn't a subject that Student Finance would fund you to study at undergrad level if you already have an undergrad degree. See:
https://www.heinfo.slc.co.uk/resources/guidance/courses-management-service-user-guide/eligibility/equivalent-or-lower-qualification-elq-exceptions/In other words, you won't likely be able to get student loans for your PGDL or degree.
I would try to get into law without doing further qualifications first (especially if you intend to become a solicitor). If you can't, then see if your employer is willing to help fund you for your PGDL (or find scholarships for it). If not, then you would either have to work for a whole year or 2 and save up every penny or do something drastic to get the funds that you would need.
What I do recommend people to do is to try to get work as a paralegal at a law firm to see if it is something you actually want to do (you don't need a lot to work as a paralegal, and A Levels + GCSEs are plenty:
https://nationalcareers.service.gov.uk/job-profiles/paralegal). If you don't like legal work, then it's not worth the time or investment to do law qualifications or try to get into the sector - it's very competitive and you have to invest a lot of money and time to get qualified (your most difficult challenge isn't the degree or qualification, it's to secure a training contract as a solicitor or barrister; law graduates are a dime a dozen, but the training contracts available are few and far between).