"Four more stops, Harry ... Three stops left now ... Two stops to go, Harry..." -- Arthur Weasley
The underground railway system in London is commonly referred to as the Underground or the “tube.” Though the names of the stations are never specified, Harry has taken the Underground three times:
On Harry’s first trip to London, he and Hagrid took the underground from an unknown surface train station (likely Paddington, though there are several other possibilities) to the stop nearest Diagon Alley – almost certainly the Charing Cross stop. On this trip, Hagrid got stuck in the ticket barrier and drew attention from the Muggles for knitting a huge yellow something or other, and being crammed into a seat much too small for him. After shopping, they made the return trip as well (PS5).
Harry and Arthur Weasley took the underground from Grimmauld Place (at a “miserable little Underground station”) to the Ministry of Magic – at a “station in the very heart of London” – for his hearing in 1995. This was Mr. Weasley’s first time on the Underground, and the automatic ticket machines were out of order (OP7).
Harry again took the Underground from Grimmauld Place – this time with Tonks, Moody, Ron, Hermione, Fred, George and Ginny – to visit Arthur in St. Mungo’s (OP22). Again their stop was described as being “in the very heart of London.” They returned by underground as well (OP23).