Please note, this tariff is no longer available to existing customers wishing to switch to the tariff.
If you are not already on this tariff you will not be able to switch to it.

Classic Pay As You Go

With Classic Pay As You Go, you pay for what you use, as you go. The minimum top up requirement is £10.

If you don't top up, or add a Bolt On at least once in any six month period, your mobile will be disconnected and you'll lose any credit on your account. If you want to be reconnected you'll be given a new mobile number.

Classic Pay As You Go charges

No data capped. Your Top Up balance will be deducted after every 20MB block of data usage or if the data session is ended (whichever happens first). There is a minimum charge of 1p per data session. The cost of each data session is rounded up to the nearest whole penny. Use O2 Wifi when you're out and about. We have over 10,000 hotspots nationwide. And use your wifi when you're at home to save on your data usage.

Source Jan 18 2018

This now is true of Three PAYG as well as O2 PAYG.