You can order a SIM for your data dongle online – just choose the standard SIM option. You'll then be on the 250MB Pay as you go data price plan. This means for every £5 TopUp you get 250MB of UK data, which lasts up to 30 days.
If you have trouble connecting to the internet with your new SIM, please ensure that the APN on your software is set to SMART.
If you need help changing your APN settings, please visit Device support and choose your device. Then select Basics >Browse the web > Set up your device for the internet.