 In 1935 , the London Passenger Transport Board ( LPTB ) announced a proposal , which became known as the Northern Heights project , to take over the LNER lines from Finsbury Park to Edgware , High Barnet and Alexandra Palace , and link them to both the Northern line at East Finchley and to the Northern City line at Finsbury Park . The construction of the first phase of this project involved extending tube train services from the Northern line 's existing terminus at Archway station , through a new section of paired tunnels under the LNER 's Highgate station to emerge south @-@ east of East Finchley station , where track connections to the LNER line were made . 
