I got a taxi, think it worked out about £6-7, but some taxi drivers will try to get more, one tried to charge me double that until I told him I knew how much it normally costs, I think it took less than ten minutes to get to from the centre. Just tell the driver you want to go to Showpark. You can also get the tram, which I think takes around the same time.
It looks like the one outside the centre is now called Showpark market.
Link to there info page
http://en.showpark.info/contact.html#taxi