This is a distance of about 10 meters with 2 brick Victorian internal walls in-between. No matter how much you spend on WiFi equipment you can't get more than 20 Mbps with high packet loss here.
Even downstairs, with no walls to worry about, only 5 Ghz is usable. 2.4 GHz is completely occupied by neighbours, and the lower 5 Ghz channels are all crowded out because of compatibility too.
I hate WiFi with a passion.