I was thinking this the other day, they had a run of turning out utter dreck in the early 2000s. The 175s, 460s and 334s, have all proved problematic in service. Didn't they have to give ScotRail two additional 334s as they'd messed them around so much? The only thing they got half right was the 390 and that was a Fiat design. Is this why they haven't featured in the UK market much since then?
Alstom pretty much withdrew from bidding for new trains for the UK after the Coradia/Juniper saga, and closed Washwood Heath with no orders after the 390s.
The 2012 new Virgin Pendolino trains/cars were built in Italy/France.
Their current range is not to the UK's taste, though the iLint hydrogen trains might get them back if the trials get anywhere.
They bid articulated trains for Thameslink, but NR took fright and they were excluded from the short list.
But today we have Stadler's articulated Flirts coming in for GA and Merseyrail, so someone has changed their thinking somewhere.
Meanwhile, Alstom's UK English Electric/GEC heritage has practically vanished, with the 390 traction package being about the last hurrah.
The new Widnes plant, however, might be the springboard for a comeback.