What if Britain's PM Arthur Balfour had moderated the Russo-Japanese War peace treaty instead of US President Teddy Roosevelt?

Russo-Japanese war of 1904-1905 was an unmitigated disaster for Russian Empire, costing them the territories and influence in northeastern China and several islands, plus the loss of two modern naval fleets.

However, it could have been far worse as the Japanese might have taken a chunk of the Russian Far East as well, if not for the efforts of Pres. Theodore Roosevelt handling moderation during the Treaty of Portsmouth.

Thus, I wonder what would happen if the US did not intervene, but more likely, Great Britain, who was nominally Japan's ally under the Anglo-Japanese alliance at the time had been the moderator under Prime Minister Arthur Balfour.

https://en.wikipedia.org/wiki/Russo-Japanese_War

https://en.wikipedia.org/wiki/Arthur_Balfour#Prime_minister