Britain's deterrent weight in an expanded Franco-Prussian War

How might the Franco-Prussian War change if Russia and Austria joined France while Britain backed Prussia?

British intervention would likely deter further entrants; Italy is the main uncertain exception because hostility to Austria conflicted with the danger of fighting Britain.

The scenario adds Russia and Austria to the war against Prussia while Britain supports the Prussian side. British entry would probably deter further states from joining because it raises the coalition's naval and economic risks. Italy is the one plausible exception: it had reasons to oppose Austria, but also strong reasons to avoid a direct conflict with Britain. No firm battlefield result is established, so the useful conclusion concerns diplomatic alignment rather than a predicted victor.