You can grab the equivalent of a year's worth of data SIMs (at 1GB per month) for as little as £45.96 including delivery. Amazon's A1Techstore sells a data SIM from mobile phone operator Three Networks, preloaded with 3GB of data for as little as £11.49 (that's just under £3.90).
You can use it on any unlocked 3G dongle, 3G phone or device (like a tablet or a 3G-capable laptop). You can use that allowance over 90 days and you don't need to register or activate the SIM card. Bear in mind as well that it is a mini, rather than a micro SIM. It is not as fast as a fixed-line broadband but is probably more convenient.
Three has already committed to introducing 4G later this year and has already enabled 3G+ (DC-HSDPA+) on its network already. Bear in mind that you will be able to use this SIM card in any Android smartphone (with Froyo onwards) and convert the later into a full-fledge Mi-Fi device that can potentially even take a microSD card slot.
It is also worth noting that the offer is best for those who occasionally use mobile broadband. Otherwise, you might ending up popping quite a few of these in an out of your device.