As you will probably appreciate, a budget of £120 doesn't give a huge range of good options. Even AMD, that normally "comes to the rescue", at the budget end, can't offer any particularly palatable choices.
Being limited, in order to give some ability to upgrade, in the future, I think using Intel, with a Pentium processor, at least gives reasonable performance, now (better than an AMD Phenom alternative), possibly Intel Pentium G850 2.9GHz. That is available, from EBuyer @ £51.44. For RAM, I would suggest using GSKill 4GB(2x2GB) F3-12800CL9D-4GBXL 1333MHz DDR3, available from Novatech @ £24.98. There are slightly cheaper options for RAM, but there's no point, to save £3 or £4.
The question then, is motherboard. If you want to keep to budget, and get decent performance, using above components, I would suggest ASRock H61M-S. That is available from Amazon @ £39.72.
If you can stretch budget, a bit, it may be worth considering a motherboard, that gives you a decent upgrade route, all the way up to something like i5-3570K, a quad core Ivybridge, with overclocking. Whilst it would be slightly overkill, with a Pentium, at present, a Z75 board would allow you, if you wanted, to step up, in future to use Ivybridge, overclocking, USB 3.0, etc. Currently an ASRock Z75 Pro3 is £74.34 at EBuyer. (You could probably get it £10 cheaper, with a bit of shopping around). Nothing like essential, but worth a thought, if you think you might want to upgrade, in 12 months, say, without having to spend a fortune, then.
thanks for the help was very useful, you said stretch the budget a bit how much were you suggesting? because i was going to spend 30 pounds on a case but i already have my older one from my acer aspire m1640 so would the extra 30 pounds make any difference?
It's a question of using the Asrock Z75, instead of the H61, which adds about £35, if you get from EBuyer. There are a couple of sites, doing it about £12 cheaper, but I don't know what they're like. I do know EBuyer are pretty reliable. What that board gives you is the ability to upgrade, to a much better processor, when funds allow, without changing mobo. Of course, you may never want to do that. I wouldn't, necessarily recommend going without a better case, to do it. Much less hassle, at least, to change a mobo, than a case, in the future. If you can't afford to do mobo upgrade, as an EXTRA, I wouldn't bother.
That set-up, using either mobo (it makes no difference NOW which), and your graphics card will make most games playable. High settings, in demanding games, like BF3, will be beyond you. It's not processor/mobo that will hold you back, from more, it will be the graphics card. You will be able to improve the GPU, quite a bit, before you find it's processor that's holding you back.
The best way to upgrade, is to alternate. One time, you update graphics, as much as you can afford. The next time, you upgrade processor/ motherboard, as much as you can. And so on.