I'm going to take a slightly different approach.
For the most part, you want to find an adequate amp that meets your needs. For the average user buying a 5.1/7.1 surround sound A/V amp, an A/V receiver with 70 to 100 watts per channel is enough.
A very popular amp right now is the Onkyo 605 A/V Reciever with about 100 watts per channel. It has all the digital options you need and it is about £350. That leaves you about £650 which will buy you a pretty nice 5.1 surround system.
http://www.eu.onkyo.com/products/product_en_5710611.html
There are other brand sof amp in the same range as the Onkyo that are just as good for roughly the same money. Sony, Yamaha, Pioneer, Denon, NAD, Marantz, etc...
Which set of 5.1 speakers you choose will depend on how much room you have and how big you are willing to let your speakers get. If because of space and personal preference, you want very small compact speakers then you can certainly get any one of several nice systems in the £300 to £600 price range, and have an additional £50 or more for accessories like wire. Remember it takes a lot of wire to wire up 6 speakers.
Many sellers have put together system packages with additional discounts.
For example: Richer Sound has a package that includes Onkyo DVD player 405, Onkyo A/V Receiver 605, and a Kef very compact 5.1 surround package 1005 for £699.95. Personally, would be willing to spend a little more and get better speakers, but if most of you listening it TV and Movies the system as configured would be nice for that purpose.
http://www.richersounds.com/information.php?cda=static&cst=homecinemasystems
Here are some samples of individual components -
Onkyo 508E 5.1 A/V Receiver 75 watts/ch @ £199.00
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/3490
Onkyo HRTTXSR505E 5.1/7.1 A/V Receiver 75 watt/ch @ £249.00
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/3350
Onkyo TXSR605E 5.1/7.1 A/V Receiver 90 watts/ch @ £399.00
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/3368
Though I'm sure I've seen the 605 for £350.00 somewhere.
Any one of these amps or similar amp in other brands would work fine for your need.
For speaker systems, here is a cross section -
Q ACOUSTICS 1010 5.1 SPEAKER PACKAGE (BEECH) @ £299.00
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/2893
WHARFEDALE DIAMOND 9 HCP HOME CINEMA SPEAKER SYSTEM @ £329.95
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/2210
MISSION CINEMA M33i HOME CINEMA SPEAKER PACKAGE (M33i + M3C2i + M30i) @ £379.95
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/2752
WHARFEDALE EVO2-AV SPEAKER PACKAGE @ £499.95
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/3397
QUAD L-ITE 5.1 SPEAKER SYSTEM @ £599.00
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/2479
There are several combinations here that will keep you well under budget, and iI'm sure will satisfy you completely.
I provide links to SuperFi as a matter of convenience and because they have a reasonable selection and they have stores around the UK. I'm not specifically endorsing them. Look around at several internet seller for similar systems. It pays to shop around. Recently I posted a link to a £500 speaker system that someone else found for only £250, so it pays to shop around.
One additional point -
"Also how do the power ratings compare, should the speakers be rated at more than the per channel rating on the amp or vice versa?"
This depends a lot on how you use your amps and speakers. If you are throwing a lot of outdoor parties and are cranking you amp up to 80% or 90% turn on the Volume Control, then nothing will save you. However, if you are a normal person who considers 'loud' to be about a 40% to 60% turn of the Volume Control, then you are probably never going to have problems.
Ideally, you want your speakers to be rated higher than your amp; so, 70 watt amp with 100 watt speakers. If you use your system sanely, then 100 watt amp with 100 watt speaker is still safe. Taking it one step farther, again assuming common sense and sanity, you can have 100 watt speakers on a 120w to 150w amp. As
Happhhitachi points out, many people do it and never have a problem. If you reach the level of 100 watt speakers on a 200 watt amp, then you are pushing your luck.
Most people don't realize that every time you turn the volume control up and hear a noticeable change in the perceived sound level, you have DOUBLED the average power. So with a very over-powered amp, one nudge of the Volume Control can be enough to push it over the level that your speakers can handle.
Generally, the speaker can and should be higher than you amp. If the amp is no more than 20% more than your speakers, you are usually not going to have to worry about it. More than 20% and you do have to be careful. Remember what I said about power, just one tiny nudge upward of the volume control at already high levels is enough to push your speaker beyond their ability. As a general rule, if you always stay below 60% turn of the volume control you are not going to have any problems.
Steve/BlueWizard