need h3lp on whether there us a deadline for asking your insurance uni to release you

hi pls advise me i have an insurance offer from reading uni and after deliberating over it today i have decided that i dont want to go there and would rather go through clearing or bet on my priority remark pushing my grade up to get my ucl firm, im wondering wether my deal with ucl as they have rejected me on ucas means i have to ask reading to release me or is it possible i could wait until i get the remark and rhen call up reading based on the remark results?or is this considered bad practice amd will it it be too late as i may ahave exceeded a deadline for asking unis to release you. pls help

Have you told UCL and Reading about the remark

I have told UCL and they said that there is a strong chance they will accept me if the remark puts me up a grade, im just not sure how to deal with reading, should I let them know I want to be released now?