CJG Now Thankfully Living In The North wrote:
Eurostar trains that run for Eurostar are maintained at North Pole
depot which is in inner north west London. You can see them from the
Great Western Main line from paddington. They use the West London
Line to near Clapham Junction and then the main line into Waterloo.

I suspect you may be referring to the Eurostar sets used by GNER for
the White Rose express services. I think they are maintained at
Bounds Green depot where most of the GNER fleet is maintained. There
are smaller facilities to deal with minor servicing of GNER trains
at Newcastle, Edinburgh and IIRC Leeds.

I knew it was in Herfordshire somewhere.......

Bounds Green depot is in the London Borough of Haringey.

Wouldn't it better to build a depot somewhere on Waterloo line?
Isn't their space around Wimbledon?

Eurostar's? No, their space is not around Wimbledon; it's at North Pole.

Or even the one by Three Bridges in Sussex? I think Gatwick Express or
Virgin use it?

That's over 30 miles from Waterloo. I think you need lessons in geography
as well as grammar.
--
Richard J.
(to e-mail me, swap uk and yon in address)