Three ups their Go Roam limits in the EU.

[Minxy]

Is this increase a monthly usage limit, so if I am in Spain for 3 months and I have 100Gb/month allowance can I use 19Gb each month, or is it 19Gb for the entire period not in UK?

Yes, you can use 19gb per month.

However you may find they stop it in the 3rd month if you have used it abroad for more than you have used it in the UK - read their T&Cs.