Tescos have permanently reduced the 1 month SIM only tariff:
£10 - 500 mins / Unlimited (3000) Texts / Unlimited Data (500mb)
£15 - 750 mins / Unlimited (3000) Texts / Unlimited Data (500mb)
This is a brilliant offer. Giffgaff need to look at this and maybe think about upping the minutes to:
300 on £10 Goodybag,
600 500 on £15, 900 750 on £20 Goodybag.
EDIT: Crossed out values as minutes might be too high for it to be sustainable.