Cheapest UK data for one week traveler
 

I'm coming to London in November for a week with daughter and friend. I'd like to use MiFi adapter (Tether 3G to all 3 of us) and I've searched a bit and found out that GiffGaff would be best but in unlimited data plan, tethering isn't allowed. They do, however, have gigabags which cost £12,5 for 3 Gb. If I buy it with someone recommending me as new user, I'll get £5 and all I have to do is top up with £10 and activate that gigabag.
Is there any cheaper option ? :???: Or maybe a little bit more expensive, but with more Gb's ?
Thanks in advance. :o

I can send you Giffgaff SIM cards, for which you will receive £5 free credit upon activation (and so do I). You might also want to consider Three, which now charges 1p/MB with 150MB for free after every top-up. However, Three's coverage isn't as good as O2's (on which Giffgaff runs). Please PM me if you want some SIM cards.

In the mean time I already ordered card from link on the forum (foreign GiffGaff orders)..