Buy Huawei E8231 Wingle - Unlocked In-car WiFi from our Mobile Broadband range - Tesco
Buy it, buy a pay-as-you-go or rolling contract sim from a phone shop.
Remove cover, slide in sim, note wifi password, replace cover.
Plug into a 'wall wart' mains-to-usb adaptor. Or any usb anywhere, including in your car (they supply the adapter).
On your computer, look for a wifi signal that says HUAWEI. Click on it and enter password.
All done, no 'techie' stuff at all.
