Would Britain? Contrary to the opiniony ou hold Britain isnt and wasnt the worlds white knight in shining armour. As long as Japan doesnt threaten Britain's sphere, why would Britain care?
Japanese expansion was a big threat to British economic interests in China, and it did cause concern. If Britain had nothing else to worry about it could cause a lot of anger.
The US spent a lot of the 30s egging Britain on to stop the dictators, including Japan. If the British did so the US case for staying out entirely would be much weaker - domestically and internationally.