Hi Rees,
At the moment, no insurance companies will
insure you for a short term period if you are not 21 yet. You could however get insured for a minimum of 1 month with
eCar Pay As You Go Insurance though. They do it on a monthly basis and there's no age restriction for that type of insurance policy. Try getting a quote from them and see if it's affordable for you, otherwise you wouldn't be able to drive (legally!), I'm afraid.