I am in exactly the same position as you. My offer was A*AA for English at Streatham but I missed it and ending up getting AAB. My insurance is also UEA. I am going to look at the campus tomorrow to see if I like it before making my decision. Is it possible for you to do this? They offer free accommodation and can reimburse travel expenses up to £50 as it is so far at such short notice for most people (I'm in Surrey).
Penryn is a lot smaller than Streatham and there is a lot less flexibility with modules; you only get to choose modules in year 3 so all year 1 and 2 modules are compulsory. However, within the modules, there is optionality as you can chose to write your essays on one aspect of the module if the rest doesn't interest you. Have you tried calling Penryn and had the course explained to you? I spoke to a student who has just finished her English Lit degree and one of the senior academics at Penryn. Its worth a try.
However, if you are still keen on Streatham, get a priority remark of your English paper and let Exeter know what you're doing. They may offer to hold your place and take you if your grade does go up.