From the TfL website...

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VICTORIA LINE: On Saturday 8 and Sunday 9 July, suspended between Seven
Sisters and Highbury & Islington, with a reduced service on the rest of the
line, due to planned engineering works.
REPLACEMENT BUS SERVICES;
Seven Sisters - Manor House (Southbound only);
Finsbury Park - Highbury & Islington (Southbound only);
Highbury & Islington - Finsbury Park - Manor House - Seven Sisters
(Northbound only);
Passengers should use Piccadilly Line services between Manor House and
Central London where possible;
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Unless there's a bus crushing plant in Manor House and a bus factory in
Finsbury Park, these buses are running empty southbound between Manor House
and Finsbury Park. If your journey was from Seven Sisters to H&I, you would
find that very annoying.