"can"

In my experience in both Portugal and the UK is that they never do.

Only train I know of in the UK that actually goes that fast in practice is the Eurostar service (that goes through the Channel Tunnel) and that's not a pendolino. A number of long distance trains services in the UK are done by pendolino trains, but the rail track is not good enough for them to go at 250km/h.

In Portugal the Alfa train that goes between Lisbon and Porto and which is a pendolino train does up to 220km/h, but the average speed between both cities is a lot less than that (around 180km/h, if I remember it correctly). No other train there goes even that fast.

Only time I ever went that fast (faster, even) in a train in Europe was with the Thalys (basically the Belgian TGV) from Brussels to Paris and back and that's not a pendolino train.

You see, whilst that tech is indeed capable of a top speed of 250km/h, actual stretches of rail line capable of safely supporting it are pretty rare.