They reportedly fixed the problems with a multi-million pound refit. But I see a lot of British troops with M16s at the moment.
The problems were various. IIRC, the placement of vents allows dirt, sand or dust to cause repeated jams. The magazine is placed in such a way that a soldier running with it close to his body can hit the magazine release catch. The LMG version was woefully unreliable too. In short, many British soldiers hated it and ot was atrociously bad in the last Gulf War.
The SAS don't use it, they use M16s. I think that says quite alot.
But like I said, things might have changed with the new version.