That would do it, but I can't see any mention of it not expiring - I'll try asking some questions in their forum.

sainsburys
 

Try Sainsburys very good and low price

It will run for one Month, and you have the choice of it recurring or buy another 5.00-7.50-12.50 online or from your phone, if you pass your month and have not "topped up" or "recurred it" it will obviously stop working untill you do.
You will need a sim card if you are not adding it to your current GiffGaff one.
Just as a point of interest for you if you do not already know, you can earn points by "yakking" on forums, even asking questions will earn. They pay out twice a year and turn the points into cash, you then have the choice of donating to a charity, having credit put on your phone or paid into a PayPal account..........I see you like to write on our forums so you could make a "bob or two" on GiffGaff. I think the record for money paid out is £23,000 yep twenty three thousand pounds thats a lot of Q&A`s on a forum, how about our club doing that? (just joking) lol.
Ken.

Oh, so that's where my £2.50 extra free credit came from - I did wonder. :D

Whats the 'recurred' part?

You can set it to recur (continues payments) to save you going into GiffGaff site to purchase another months worth of data credit.
I buy mine on the site because I am usually flitting from Phone to Tablet with any data, it becomes expensive to have to buy 2 lots running at same time and a hassle swapping sim cards back and forth..........what I`m saying is............I might go a month or two when I don`t need any data at all on either device.
Ken.

I see, there lies the problem - mine could go for many months unused, so I would be paying for it and not using it.

In that case you would just buy one months data plan, and if you needed it for one more month go online and buy another, you don`t have to wait untill the one you have runs out to buy an extra month, it would start when the current data credit finishes without a gap....if you do not need any more data..... ie; Sept, Oct you just don`t buy none.

When I say MONTH, it can be any part of the month and will expire approx 30 days from the start day.
I feel like a salesman for GiffGaff :} if you and I had done this chat on their forum we would have earned a couple of "bob"

Giffgaff
 

Harry

Giff gaff used to do a plan that was data only with no limit on time

This has been discontinued

I don't think there will be any providers using that plan now
I would imagine your options would be to use the lowest monetary plan so you don't loose as much or the plan that suits your Internet usage at home and cancel your home Internet ( although it depends on what you use at home)
Regards
Steve

Harry I'm assuming the data requirement is for when you're away in your caravan.

Remember Giff Gaff runs on the o2 network which sometimes struggles to get 3g in all areas, especially low population ones. I'm currently in deepest Cornwall, my o2 network phone can only manage gprs, whereas my tablet on 3 is receiving 3g/hpdsa. Granted you may be using an antenna with your dongle which would help with reception.

My solution was to trawl ebay and buy the cheapest 3 mobile broadband sims with 30 days/1gb data I could find, currently using one that cost £7.00 and have another ready to go that cost £5.31.