I was going to leave it to a shop to order all the parts in and replace the old parts but he was trying to pull the wool over my eyes by charging me £70 more than the actual price of the parts + the £50 labour cost he wanted.
Your case will allow up to a full-ATX size motherboard, which is what that ASROCK board is. You should be fine.
Small shops always want to make money off the parts purchase and also the labor. So don't expect to get a deal for a custom installation. They also have certain vendors they buy from so you may actually find better deals shopping around yourself. The best deal is to do it yourself. It really isn't that hard to do, but as with anything you can run into issues and have to deal with them yourself. You can always shop around at other shops or if you know a buddy who is computer build savvy he will usually charge you much less. Me personally, I charge for labor only and you would buy the parts for me.
Also, what are you using your system for? If it is for gaming I would seriously look at upgrading your graphics card. A GTX260 just doesn't cut it anymore. It would be good for very light games or playing older games, but that is about it.
Good to hear. Some of those little shops are very devious in their business practices. However, there are others that are actually very good and do good work. So it makes sense to shop around and feel comfortable with who you are going too.
I would not expect your 260 to run most modern games are any reasonable setting, especially at a 1080 resolution. There are some games that have very low requirements that it may be ok with, but not all that many. I would also skip that 560 and go to the 600 series. I would highly recommend doing everything in your power to get to the GTX660 instead of a 650TI. Even if it means getting a lower clocked i5. The performance is very much worth the increase in cost compared to having a faster clocked i5.
What I mean is I would get a GTX660 even if it meant not getting an i5-3570K and getting something like an i5-3470, or another lower clocked I5. It does not have the unlocked multiplied that the "K" model has and is 300MHz slower, but really that isn't going to effect your gaming all that much compared to a GPU upgrade.
While that isn't a power supply I would personally choose if had the choice, it should do the job just fine. A fully loaded system with a GTX660 is just under 300W at load. http://www.anandtech.com/show/6276/nvidia-geforce-gtx-6...
It is not even an 80plus power supply so I wouldn't want to get anywhere near that 650W max, but your configuration should be just fine. I would not want to do any crazy overclocking, but moderately should be ok. It's one of those items that may be a good idea to replace sometime down the road if a good deal comes along. Power supplies are one of those things you can take from system to system as you upgrade. So it's something worth investing in. I'm still running the same PC Power and Cooling 750w that I've had for 6 or 7 years. It's seen many of upgrades and I picked it up for something like $50 off Newegg at the time. http://www.pcpower.com/power-supply/silencer-750-quad-c...
The best times to upgrade are when you keep a window of opportunity open and keep your component choices flexible. Just watch Newegg and wait to pounce. My coworker just built her entire system with a i5 3570, Asus wifi motherboard that came with free RAM and intel 120SSD. She got something like $150 in savings by selecting the right components and waiting for the right time. Just watch for deals because they will eventually pop up.