Only take a gap if you genuinely really want to go to ICL because if you choose one of the other unis, you will always ask yourself 'what if i had reapplied and got in'
In terms of IB, Warwick is your best bet but the other 3 unis you mentioned are semi-targets and will not disadvantage you. At the end of the day, if you can get internships and have good extra curricula activities, you're not going to be rejected based on going to one uni instead of another (seeing as all of them are good uni).
If you are determined to go to ICL, it'll be worth the gap to get to your dream uni, but all your other choices are still great!