Is 40GB internet allowance per month enough for my household?

In my house we have two laptops and two iPhones which are connected to the BT Home Hub. My brother and I browse the internet, we don't download games and rarely download applications (unless it's from the apple app store for my MacBook). Our browsing is quite heavy-use though. I'd say I spend around an hour every night on my laptop, and my brother spends around four hours.

WIll 40GB be enough?

If you don't download a lot of movies or games that take up a lot of traffic, it'll definitely be enough.

In my house there are two adults and two teens. I get annoyed with the teens sometimes over their use and switch the hub off. We still get through more than 40 gigs though. Go for the unlimited package, its not that much more.

I would just always go for unlimited because it's not worth the risk. I would use that up just on YouTube uploads. Also, you can use the internet to save you money, so if the money you save is more than the cost of unlimited access in a given period, it's not even worth not having the internet. Also, you get free roaming with BT Fon, and as it happens i'm using that right now. When we were on the lower level, we were able to exceed it by just watching Wimbledon.