Seeing as your in the UK, have a look as Halford's as there Professional range is pretty good, they also come with the ball bearing runners.
The 7 draw top box & 5 draw roll cab are on package offer for £200 at moment.
There's also the Industrial range for something a bit stronger, they look pretty sturdy to but there more pricey.

Clarke boxes from Machine Mart are also good if you start from the heavy duty plus range & work your way upwards, slightly more expensive then Halfords.