Was looking for exactly this - the old version Vodafone TopUp and Go Mobile Broadband where £15 gets 1GB of data with no time limit (use it once every 270 days to keep alive I think). I was in the Currys.Digital shop in Beverley (E Yorkshire) & saw the pack with 1GB written on the front (picture can be seen at http://www.ciao.co.uk/Voadfone_Mobile_Broadband__Review_5834457)
- I was in two minds whether to price check it & luckily took the plunge -when he said £15 I couldn't believe my luck (I was looking at paying £15 for a modem & £8 for this specific type of sim on eBay). Its for my uncle & he specifically wanted the no expiry type.
The receipt says "Vodafone K3565 1GB Prepay" & 0000003745.
Good luck if this appeals to you - probably a case of worth checking your local DSG store if passing rather than travelling to one on the off chance.