Baby oil may help some when topically applied in the ear, but it can be difficult for it to be completely effective in getting rid of the mites. Often the mites will re-emerge once the baby oil isn't reapplied. My opinion is that it's better to use one of the recommended rabbit safe antiparasitics, which will kill off the mites completely, when used at the correct dose and frequency. Even better is to have your rabbit checked by a knowledgeable rabbit vet for a proper diagnosis and treatment.
Ivermectin and Revolution/Stronghold (selamectin), are 2 listed as rabbit safe, which is important to only use rabbit safe products, as some can be fatal to rabbits if used. My preference is the Revolution spot on topical, for effectiveness, ease of use, and safety (some rabbits can be more sensitive to the effects of ivermectin). It usually only requires one or two treatments. Beaphar spot on is available otc in the UK I believe, Revolution spot on or ivermectin as injectable, is prescription and would require a visit to your vet.
https://wabbitwiki.com/wiki/Mites
Medirabbit: ear mites
One thing to keep in mind, is that a rabbit showing irritation and excessive scratching at the ears, doesn't necessarily indicate ear mites. It just means something about their ears is bothering them. It certainly can be ear mites, but it could also be debris stuck in the ear or a sign of an ear infection. Ear infections can be very dangerous for rabbits to have, and need to be properly evaluated and treated by an experienced rabbit vet.
Medirabbit: ear infection clinical signs and treatment
If treating for ear mites doesn't work, if there are other more worrying symptoms, or you're uncertain what's going on, it would be best to have your rabbit properly examined by a knowledgeable rabbit vet. A recommended one near your listed profile location, is Beaumont Sainsbury Animal Hospital Camden, or check the list for another recommended rabbit vet near you.
https://rabbitwelfare.co.uk/recommended-rabbit-friendly-vets/