Currys / PC World are (again) selling Three network data SIMs with 1Gb data valid for 30 days. Now £0.97 each with order and collect.
2 weeks ago they were reduced to £1.97 from £7.99 but now (if you can find them) they are £0.97.
I have used these before and they are just 'plug and play' in a Mifi device or a tablet.
If you want a fairly cheap, quick data fix then these could be for you. They also work abroad with the Feel at Home benefits - which doesn't include streaming of shows or music channels but does all email checking and internet browsing etc. Usually slow but it does work
Might be of use to someone.