There are quite a few MMI free webinars (Leicester, Exeter, Imperial, Road2Med, etc.). KCL does a great free webinar series from Feb - Jul, which I believe includes interview prep, and they don't ask for contextual factors apart from being from a state school. Then there are many free summer schools that do include interview prep in person (Bristol, Oxford, Uniq, KCL, and so on.. but they usually require contextual criteria.
Imperial actually do a lot of WP activities in London schools and online. They also organize a few summer schools (but with contextual criteria).
On fairness... There are tens of companies doing interview/MMI prep for a hefty fee - we can't afford those - so we will grab whatever we can. DD has not applied to Imperial , but 3 of the med schools she has applied to do MMIs.
One of my DD's friend is in year 12, she's already done 4 weeks of medical experience, arranged by a relative who is a doctor. My DD has struggled to find work experience placements, but she found one in the end, and she also found a volunteering role. Her friend's indie school does 'free' MMI mocks and has a 'med school' advisor. DDs school didn't even have a medsoc until this year, when DD created one :) The parents of DDs friend have paid £7K for an expensive 2-week summer school, as they don't qualify for any other summer schools, and they feel it's unfair that they have to pay 😂. £7K seems nuts to me, but then DD did a 5-day Gold DofE med residential at Dorset Hospital, which we paid £800 for, which we could afford. It wasn't free, but some people would think that's too much... And perhaps they will judge it as being unfair.
I think we all do our best with what we can afford / can access where we live. And it's good that med schools have contextual offers so that those without resources have a bit of of an advantage over standard applicants.