Sutton Trust has both summer schools, programmes about specific career routes and then also Sutton Trust Online, which is information across 6rh form and into uni slightly on everything application based to apprenticeships or uni, for medicine, dentistry, vet me, Oxbridge. Even stuff on wider skill development courses, help with personal statements, workshops/webinars all about various topics from those who've done it etc, those talk to our alumni online things.
So I'd make sure to look at each of the different programmes and the criteria. The ones Aelin mentioned tend to individual university programmes, which can get entry grade reductions and also to do university style lectures etc. These criteria are down to individual univeristy and the best way to research is reading through each university's specific criteria on their website. They may also have different 'strands' of a program with each one having different criteria.
SMF as in the name is the Social Mobility Foundation, so they tend to have more criteria about w/c, deprived/BAME, but I'd check as they have different programs based on some careers people are aiming for, and some of the programmes include a free residential doing work experience at a company in that space.
On the whole for work experience (assuming they don't have other contacts etc or connections, as I didn't at all), the best way I found is never be scared of a cold email. Be very nice, drop in bits to show you've done your research on that specific company/industry (law), or person. Also definitely show your accomplishments and why you want to do it in general and then why that place. You only need one person to reply and it can work for medicine or other things as well.
My friend and me went through the websites of the 3 nearest hospitals, and we went through the consultant page, with the consultants per speciality and emails. Picked those in specialities she liked and cold emailed as many as we could over a few weeks. One doctor replied and she got 2 weeks of work experience in urology. She really enjoyed it even though urology was the one she thought she wanted the least (out of the ones she picked, as in specialities). But she actually said they were all so nice, talked to her about application stuff, and also she was pleasantly surprised by this. She was applying for med, and this was in Y12.