If I were travelling from Berlin to London by train in the
nineteen-thirties which London station would I arrive at, Victoria or
Waterloo?

Dear bow33-ga 
From my research, I can state that the end of the journey would have
been at Victoria Station as this had become known as the ?Gateway to
Europe? and had boat trains to and from Calais, Dieppe, Flushing and
Ostend. Waterloo, meanwhile, was the link to Southampton and the
Cunard liners, among others.

This is an extract from a description of a German boy?s visit to England in 1935.

"The first part of our journey through Germany, along the Rhine, and
through Belgium passed very quickly. Early in the morning we arrived
at Brussels?When we arrived at Ostend, the boys who had got tired
became fresh. When we had passed the customs, all the boys rushed upon
the deckchairs...We crossed the Channel on a Belgian ship, Prince
Baudouin...Soon the steep cliffs of the English coast appeared. At
half past one o'clock we left the ship, passed the customs, and
entered the very luxurious, comfortable, and quick train to
London?Before we crossed Victoria Bridge we saw the Tower Bridge; and
the Tower itself looked grand as it rose dark and majestic above all
the surrounding buildings...At Victoria Station we were received by
the very kind school-masters and our friends."
http://www.oldmonoviansassociation.org.uk/text/exchangegermany1934.htm

This is an account from 1936 of a journey to Sweden in the reverse direction.

Swedish Educational Tour -  May 1936
"The party of seventy-nine left Victoria Station at 10.20 a.m. en
route for the Continent via Dover and Ostend...Our journey lay through
Bruges, Ghent, and Brussels. Here our train was reversed and being
drawn from what was the rear end on the journey from Ostend, we left
Brussels Station and were soon passing through the Ardennes Country on
the Liege and Herbesthall and so on across the German Frontier to
Aachen." Later, they went via Hamburg, Dusseldorf and on to Bremen.
http://www.lococarriage.org.uk/1938swed.htm

A little before your period, but in 1912, the artists Alma Tadema died
in Weisbaden and his body was conveyed to England via the Flushing
Boat Train to Victoria Station.
http://www.artrenewal.org/articles/2001/Alma-Tadema/tadema10.asp


History of Victoria Station
"Gateway to Brighton, Europe and ? via Southampton ? the world,
Victoria Station was a proud Victorian achievement. Before long the
new South Eastern company had developed the short sea crossing routes
to Calais, Dieppe, Flushing and Ostend, almost as if they had foreseen
the Great War of 1914-18."
http://www.christopherlong.co.uk/pri.victoria.html


Search strategy
"train" "victoria station" germany 1930..1939
://www.google.com/search?q=%22train%22+%22victoria+station%22+germany+1930..1939&hl=en&lr=&ie=UTF-8&oe=UTF-8&start=0&sa=N
and other searches to check the position of Waterloo in continental train travel

You gave me the answer I was looking for, thank you

There are lots of Google search results for boat train Victoria, and
not for Waterloo; the consensus seems to be Victoria:

" the only passenger coaches ever to be physically ferried across the
Channel were the London-Paris (and for a while, London-Brussels)
sleeping cars of the 'Night Ferry', which started in 1936, was
suspended a few years later for World War II, then ran after the war
until the withdrawal of the 'Night Ferry' in 1980.  Orient Express
passengers for London have to leave their sleeping-cars at Calais
Maritime and board a ferry for Dover, where a British Southern Railway
'boat train' is waiting to take them non-stop to London Victoria."
http://www.seat61.com/Orient%20Express.htm

"The painting shows the Twickenham Ferry, which was one of three
ferries built to carry 12 sleeping cars or 40 loaded goods wagons.
Passengers could board a train at London Victoria, and then retire to
their carriage on board the ferry at Dover, to sleep the rest of the
journey to Paris. The train ferry dock at Dover was built for the
Southern Railway in the early 1930s, after a failed attempt to build a
railway tunnel under the English Channel."
http://www.nmsi.ac.uk/piclib/imagerecord.asp?id=10283090 

"Platforms 1 - 8 are in South Eastern and Chatham Railway's part of
the station, and was  the 'Gateway to the Continent', with the boat
trains, night trains, Golden Arrow and Orient Express all operating
from here."
http://www.touruk.co.uk/london_stations/victoria_station1.htm

Owain

Instead of travelling via Belgium it was possible to travel by boat
from Hoek van Holland to Harwich, and then by train from Harwich to
London, arriving at Liverpool Street Station.

1939, "train journey along the Rhine valley" - Harwich - Liverpool Street Station:
http://www.christadelphiansisters.org/JIM.HTM

1938, "overnight from Hoek van Holland to Harwich":
http://home.t-online.de/home/RIJONUE/sincla2e.htm