giffgaff are increasing their basic PAYG rates to 25p per minute and 10p per text, data now confirmed to be unchanged at 5p per MB.
I would just like to remind those who operate their SIM on a basic PAYG basis, and, who will be adversely affected by this increase, that there are still lower cost alternatives available.
1pMobile charge only 1p per minute, text, and, MB data, and, operate on EE's network. Minimum top up requirement is £10 every 120 days (4 months) i.e. £30 per year, otherwise you lose your number. UK based customer support, fully itemised usage, and, excellent feedback ratings. Can buy data boosts from £6. Can currently use same 1p tariff abroad in 46 EU destinations. I use 1p Mobile myself. Cashback is possible via Quidco/Topcashback, or, I can let you have a referral code for £5 free credit.
P.s. 1pMobile have now set up a dedicated page on their website with relevant information, https://www.1pmobile.com/giffgaff/
Three PAYG - EDIT From 12th March 2020 Three have changed their PAYG rates to 10p per minute, 10p per text message and 5p per MB. Existing customers retain previous 321 tariff of 3p per minute, 2p per text, and, 1p per MB data. Does not work with 2G devices. Once SIM is activated you can top up by just £5 online. Use phone, chargeable, at least once every 180 days to keep SIM active. Can currently use 321 tariff abroad in over 70 destinations, including, USA, Australia, and, New Zealand. Add-ons of mins/texts/data starting at £10 can also be purchased, should you ever need one e.g. travelling where there is no WiFi.
Asda Mobile charge 8p per minute, 4p per text and 5p per MB data. They operate on EE's network. And, taken from their FAQs, "As long as you use your phone at least once every 180 days your credit will never expire and your account will always remain open." You can also buy bundles if you need to, and, you can currently Roam in 50 EU destinations on this tariff.
Tesco Mobile Lite tariff charge 8p per minute, 4p per text and 10p per MB data. They operate on O2's network. I have confirmed with their chat service that you just buy a normal payg SIM and then switch to the Lite tariff, info here, https://www.tescomobile.com/help-and-support/pay-as-you-go/getting-started/pay-as-you-go-lite-call-charges. You need to use your phone at least once every 6 months to keep your SIM active. Can currently use in 48 European destinations at same tariff.
The Phone Co-op Mobile never heard of these before. They operate on EE's network and charge 8p per minute, 4p per text and 10p per MB data. However, charges for calls/texts to other Co-op mobile customers are half price at 4p/minute and 2p/text. Bundles are also available starting from £5. (Edit: they have no 4g coverage)
And, although O2 have withdrawn their Classic PAYG 321 tariff for new users, until stocks run out, you can still purchase SIM cards/SIM cards preloaded with credit on eBay, on this tariff. Just double check with the seller that it's definitely the Classic PAYG tariff before you purchase.
Please feel free to add more.
Thank you to andy69 who has suggested
"Another cheaper alternative is to get a Tesco calling card and use a 0800 access number."
And autobox who has suggested a Three data reward SIM which gives the 321 tariff and 200mb data every month. Minimum top up is £2. If you travel abroad you can use the normal 321 tariff in over 70 destinations, including USA, Australia, and, New Zealand. You can also buy a data add-on with this SIM. Read about it here https://kenstechtips.com/index.php/three-data-reward-sim
You can order a Three data SIM for free, here, https://www.three.co.uk/free_sim_mbb/order
NB see edit above regarding Three PAYG price change from 12th March. This apparently may not affect the data reward SIM, although I can't confirm
There is some useful information on comparison of rates, keeping your SIM active, and top up methods, available on this website,