@Zendadaist I'm pretty happy with #1pMobile (who use the EE network). Their PAYG data bundles are slightly cheaper than #Three (£10 gets you 50GB/30 days).
The only problem I've had was a hard time getting any data through in Oslo when the Pride Parade (100k attendees) coincided with the Tons of Rock music festival (150k attendees), presumably because the cheap MVNO gets lowest priority when roaming.