MTB for beginner?

I've been googling around for a new MTB for about a couple of weeks and have hit a wall. I have been road cycling for two years but want something else to keep me busy over the summer and to break things up a bit. My max budget is £450. I don't have a whole lot to spend as I only have a part time job.
I used to avoid Halfords like the plague but it seems the only option right now plus these bikes don't look all too bad..
http://www.halfords.com/webapp/wcs/stor ... yId_165499
http://www.halfords.com/webapp/wcs/stor ... yId_165499
My knowledge of mtb is very limited so it's hard for me to see a difference between these too? Any other suggestions greatly appreciated!
I used to avoid Halfords like the plague but it seems the only option right now plus these bikes don't look all too bad..
http://www.halfords.com/webapp/wcs/stor ... yId_165499
http://www.halfords.com/webapp/wcs/stor ... yId_165499
My knowledge of mtb is very limited so it's hard for me to see a difference between these too? Any other suggestions greatly appreciated!

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I'd go and sit on one, see how it feels.
VOODOO CANZO
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Of course second hand is an option, but given the OPs limited knowledge I'd be careful: buying new with the warranty and aftersales is often worth it.
VOODOO CANZO
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Thanks for the responses though guys!
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VOODOO CANZO
Come and see me at https://www.facebook.com/biketyke/
VOODOO CANZO
Come and see me at https://www.facebook.com/biketyke/
edit: Decided the charge is just too expensive, good deal but don't really want to spend that much.