Karl,
Since you are under 21 of age, you will not be able to get temporary car insurance which covers you for a period of 1 to 28 days. However you mentioned that you are looking for a month's insurance and there's a company which will do just that. If you go to
eCar Pay As You Go Insurance, you will be able to get 1 month car insurance to suit your needs.
Let me know how it goes.