I applied for a visa with my teacher as an accompanying adult and my visa took longer than expected. When the time came for the trip, my visa wasn't ready yet so my teacher went to the UK without me. I was wondering if I could go alone with a consent form proving that she is already in the UK.
No do not do it. How do you prove to immigration at the airport definitively that the adult is in the UK?
The adult listed on your visa is supposed to take care of your well being throughout the trip and not just facilitate you with an entry. If you remain there and the said adult leaves the UK you/they might have trouble going to the UK again