I just got this PC. Its one of the best PC's I have ever seen for the money.
I got some upgrades for it such as RAM, over clock and cooler...however I wish I got a better card. Don't go for the stand card on it, pay the extra £50 for a better card. Trust me you will not look back.
With that said however, UK gaming computers understand that you may want to upgrade your PC in the future so they will let you do it yourself if you contact them first and tell them what you are doing. Make sure you keep them updated on everything though!
The best part of it all was the staff. They are really really really nice and helpful. I was on the phone to one of them chatting about general updates and cards and he seemed to be really enjoying the talk himself. Most of the time you are just a number....however not with these guys. They seem to care about you and your new rig.
A small note before I go however, this case and standard fans are VERY loud. I had to call them up and say to them that I needed to change the fans because they were so loud. UPGRADE the case and the case fans.
If you need any help just call them up and they will give you the best advice!