Not sure if this works in the UK, but noticed this interesting post about how to make the best use of the XBL Family Pack over on lifehacker.com. Link is here or read content below (would be interested to know if anyone has tried it!)
Xbox live Family Packs... AKA... you and four friends on the cheap.
Microsoft offers a family fun pack... me and a friend decided to go in together on one with our sons. It basically works like this...
1. Pick someone to be a primary.... take other accounts/recover accounts on that persons Xbox.
2. Have that person purchase the Xbox Live Family pack... that person will get credit for all the time he has left on his account... roughly $5 a month.
3. Once that person signs up they'll be able to add members. It will walk you through how to do this. It's pretty easy.
4. The best part about it is you get an additional month added to your account for every two months you have left... and they round up. So if you have 2 months left for 1 person... you now have 1 month for four people.
Once set-up is complete then you can recover the other accounts at their home Xbox's.
That's it. With the time we had left... plus the original discount... we ended up with 21 months of Xbox live for 4 people for $80. When we renew... it's only $24.25 per person or roughly $2.025 per month. Pretty good deal.