Magpie Electricals

Magpie Electricals was a radio and television shop located on Mafeking Terrace, Muswell Hill, London. In 1953 an alien called The Wire contacted the owner, Mr Magpie, to help her get a physical body. (DW: The Idiot's Lantern)

Although Magpie himself was killed by The Wire, Magpie Electricals survived the loss of it's proprieter, and continued to exist well past the 1950s:
 * It appears when the Doctor flicks through various websites on a mobile phone. (DW: The Runaway Bride)
 * Martha Jones had a Magpie brand television in the early 21st century (DW: The Sound of Drums).
 * Sarah Jane Smith's computer was a Magpie Electricals brand (SJA: The Mark of the Berserker)
 * The alien cruise liner, Titanic had a Magpie-brand microphone, though it was not known if this was a genuine Magpie device or a replica. (DW: Voyage of the Damned)
 * Wilfred Mott had a Magpie branded television, which he had when he sold Newspapers on Christmas Eve 2008. (DW: Voyage of the Damned)
 * The monitor and the typewriter in the reconstructed TARDIS' console room had Magpie's Electricals brand on them. (DW: The Eleventh Hour) 
 * A roadblock in Starship UK has a sign saying Magpie's Electricals above it. (DW: The Beast Below) 

Behind the scenes
The use of the Magpie Electricals logo is something of an inside joke for Doctor Who's design team.

This was revealed in an episode of Doctor Who Confidential (Doctor Who Confidential : Call Me the Doctor).

The exact nature of Magpie Electricals is a mystery, as they have been seen on a Sto ship, a TARDIS and a 29th century vessel.