Did the Northern Line ever got to Finsbury Park? Yes & No.
Known as the Great Northern Railway (GNR) back in the 30's when it was decided to electrify the GNR which ran from Finsbury Park via Highgate to Alexandra Palace and make it part of the current Northern Line, along with other extensions such as Mill Hill East to Edgware and Edgware to Bushey Heath.
GNR was eventually taken over by London Underground in the mid-late 30's, still running steam engines it was intended to be electrified as planned to join up with the LU network. Some work had been done leading upto Finsbury Park from Highgate, but WW2 halted the expansion.
The expansion didn't get enough traffic to warrant electrification after the war and continued to run steam until 1954. Now the tracks have been lifted and turned into pathways and nature reserves.
So NO, the Northern Line did not go to Finsbury Park, but yes, it almost did!
There was a tube railway built from Finsbury Park to Moorgate, opening on 14 Feb 1904. It was built to take mainline trains, as there was an idea of running Great Northern Railway trains down it to Moorgate, but this never happened. Originally independent, it was taken over by the Met, and so became part of London Transport in 1933.
Under LT, this line became regarded as a sort of branch of the Northern line. It was printed black on the Journey Palnners, and appeared on the line maps in Northern cars. It was known as the "Northern City Line"
At the 1923 grouping of mainline railways, the LNER took over the old GNR. Its lines included one from Finsbury Park to Barnet and Edgware via Highgate, with a branch from Highgate to Alexandra Palace. LT developed plans to extend the Northern from its terminus at Archway (then called Highgate) to East Finchley and then electrify the LNER lines to Barnet and Edgware, and extend from Edgware to Bushey. Another part of this plan was to link the Northern City line to the LNER at Finsbury Park, and electrify the LNER tracks from there to East Finchley and Alexandra Palace.
The war started before the work was complete. The new tube was brought into use from Archway to East Finchley on 3 July 1939, and electrification was extended to Barnet on 14 April 1940 and to Mill Hill East (mainly to serve barracks there) on 18 May 1941.
After the war, a "green belt" was established round London, which meant that the extension to Bushey would never have paid. It was abandoned, and the depot buildings at Aldenham became LT's bus overhaul works. Because of restrictions on capital works in the post-war austerity, the LNER steam trains staggered on from Finsbury Park to Alexandra Palace, with an interchange with LT at Highgate. The service became more and more sporadic, and eventually the line closed.
LT never took over the LNER lines. The LNER still owned them, and it also owned a number of the 38ts cars (as shown by a plate on their solebar) because they ran over LNER track. Well after nationalisation, BR transferred the tracks to LT.
Getting back to the Northern City line, on 3 October 1964 it was cut back to run from Moorgate to Drayton Park because its platforms at Finsbury Park were needed for the Vic/Picc interchange. And then in 1975 it was transferred to BR and main line trains started to use it to run to Moorgate, as had been planned more than 70 years earlier.
The Antipodean has it correct down to the finest detail: impeccable.
All I can add is that I used it daily from Finsbury Park to Old Street in the early 60s, and was very unchuffed when they cut it back to Drayton Park and we had to use a bus link. ****** pain that was!
Once the Vic opened it was much easier: cross platform change at FP to Vic, change again at Highbury to Northern City,- no problems!
My paternal grandfather was a driver on the original line between Finsbury Park and Moorgate before WW I; unfortunately he died on the Somme during the war. Somewhere I have a picture of him on the open-fronted stock, must try and find it sometime (the depot was in the open at Drayton Park). His name (William Hales) is engraved on the Metropolitan Railway war memorial adjacent to platform 5 at Baker Street Station.
I grew up in Highbury, and used the Northern City line when it ran the 1936 stock with the motor compartments behind the cabs. The original Highbury & Islington station entrance can still be seen on the opposite side of Holloway Road from the current Station (which was simply the NLL station before the Victoria Line was added). There was also a back entrance on Highbury Crescent. There was a lift (no escalators) and a spiral staircase.
The timetable freaks might like to think about what kinds of services might be running on the Northern if the plans had been fulfilled. What the 1949 map does not show clearly is that trains from Moorgate via Finsbury Pk would also go to E Finchley, where there would be cross-platform interchange with the Camden Town trains. Whether they would go beyond E Fin is doubtful, because of line capacity problems between E Fin and Fin Cen.
But Fin Cen was also to be rebuilt with four platforms and a smart new station below Ballards Lane bridge. You can see a bit of trackbed for the fourth line behind the north end of the City platform. Maybe LT had in mind that at some stage they would quadruple the E Fin to Fin Cen section, but I have not seen this documented,
The extended Northern would have given opportunity for some splendidly complex services. But given the drive to simplify services for better reliability, I wonder whether it would have ended up as operating as three separate services: E Fin and Al Pal to Moorgate; Bushey to Kennington via Golders Grn and Charing X; Edgware and Barnet to Morden via Kentish Town and Bank.
Mmm... Edgware to Kennington could be done five different ways:
Via Mill Hill, Camden Town and Bank Via Mill Hill, Camden Town and Charing X Via Mill Hill, Finsbury Park and Bank Via Golders Green, Camden Town and Bank Via Golders Green, Camden Town and Charing X
And people think the existing Northern line is too complicated!
Yes although the 'Via Mill Hill, Finsbury Park & Bank' option would have involved a change of trains at Moorgate, since there were no plans to link the Northern City With the Bank Branch at Moorgate for through services.
First, my congratulations and thanks to all who make this site possible - having lurked for ages I've finally registered since I thought I had something to say on this thread.
As far as the overground section is concerned, it was originally built to provide a railway to Alexandra Palace (not having a copy of Alan Jackson's magisterial "London's Local Railways" to hand I could be wrong). This is why it didn't properly serve the local centres of Crouch End or Muswell Hill - even so, it had some pretty severe gradients for steam locos...
In the 1970s there was a fierce local debate as to whether the trackbed should be used for housing or parkland - in the end the answer was a bit of both (I remember defending the scheme on local TV news as I was a Haringey councillor for a very few years).
One of the might-have-beens is whether the line could have been converted to a tramway - after all, Haringey could as easily have promoted a private Bill as Croydon later did. Indeed, had it taken Ally Pally over from County Hall earlier than it did, this might well have happened. However, as I have mentioned, the line of route isn't particularly appropriate with walks of 400-600m to both Crouch End and Muswell Hill Broadways involving stiffish climbs - not quite as bad as High Barnet, but that sort of thing.