Peter Rewko, President of the Association of Ukrainians in Great Britain, pledged the support of British Ukrainians to Ukraine.
The UK has provided military aid to Ukraine and put diplomatic pressure on Russian President Vladimir Putin to recall his troops.
The date of the demonstration - January 29 - is a significant date for Ukrainians because of the Battle of Kruty 1918, which saw 500 hastily-organised students hold out against a 4,000-strong army of Bolshevik Russians.
Although many of the students died, the delay allowed the then Ukrainian government to sign the Peace Treaty of Brest-Litovsk. The students are regarded as heroes of Ukraine because of their self-sacrifice and courage.