The Eurostar is actually smaller (read: narrower) than European rolling stock. This is due to the size of British trains. The British refused to build a dedicated line for the Eurostar's journey from the Chunnel to London. No, they decided, far better to make one of the most advanced and powerful trains ever built share the line with the ancient, rusting third rail slam door stock used south of the Thames. Had the train been European size, it would have had huge unsightly grind marks where it had shredded against the British platforms.

The Eurostar also has multiple pantographs to handle the varying catenary heights and voltages of the different countries it visits. Again, because of the UK, it has to have third rail collection shoes as well.

In the UK the train is restricted to under 100mph as neither the third rail collectors nor the tracks would survive a higher speed.

Several Eurostars were also hired by GNER to fill in the gaps after several of their Class 92 trains crashed. Their depot, which I believe is called North Pole Depot, is located west of London, you'll see it as you near Paddington. It's quite bizarre seeing a freestanding Eurostar nosecone sitting outside the storage barns.