To quote their email:
"Due to a wholesale rate increase from our roaming partners, from 15th October we will be introducing roaming restrictions to all customers with our BIG DATA bundles of 200GB.
This will mean that whilst you can enjoy the full 200GB when in the UK roaming will be restricted to 100GB per month which is still way more generous than many of the big networks out there!"
"Due to a wholesale rate increase from our roaming partners, from 15th October we will be introducing roaming restrictions to all customers with our BIG DATA bundles of 200GB.
This will mean that whilst you can enjoy the full 200GB when in the UK roaming will be restricted to 100GB per month which is still way more generous than many of the big networks out there!"