Egh, I dunno. The rendering skill of the portrait is decent, but like a lot of the popular realism art in the UK, it shouts "photograph". It's devoid of any emotion or character and is pretty, well... boring. There are many artists in the UK that could've handled the job much better.
Edit: Not trying to come off as too whiny. I think it's a good painting. I guess with such a big commission like this it's natural for it to be open for heavy criticism, given that it should be showing off the best of what's out there. The main thing I really just don't like is the scale like Elwell mentioned. It turns it from a portrait to pop art.