You could always try to come to an arrangement with a neighbour to share their broadband,
If they can cope with using a smartphone then a truly PAYG SIM card package like "3"'s 321 is another option ( data is 1p MB , and topups dont expire).

http://maps.thinkbroadband.com/#!lat=51.178868985199...

Even has FTTC and evidence of users upgrading from TalkTalk with ADSL2+ upload speeds to the 80/20 fttc service

Do you have an iPhone?

If so you could buy a little wireless dongle for your desktop computer and connect up through the phone via internet tethering when you need it.

I see you've replied to MrSaffron, I guess you meant to address the OP
FWIW It's not just iPhones that can create wifi hotspots, Android phones (and I'm guessing WP) can too.

I agree this could be a solution if they can get on a decent mobile package for their limited needs.