Hornby
Hornby is probably the most famous manufacturer of electric trains in England and has a history in train toys that predates the electrification of the hobby. Hornby's original railway sets were powered by clockwork engines, but in 1925, Hornby introduced an electric train that could run on a power supply of 100 to 250 Volts. In 1938, Hornby introduced the "Duoblo," or OO scale, but production ceased during WWII and did not pick up again until after the war. Ownership of the company shifted several times, but as of 2011, Hornby trains are still in production.
Tri-ang Model Railways
In 1946, Rovex Plastics Ltd. was founded and at first made toy cars but began producing plastic electric trains in 1950 with an OO set sold for Christmas. In 1951, the company was bought by Lines Bros., which changed the company name to Tri-ang. In the late 1950s and the 1960s, Tri-ang dominated the market with OO and HO scale trains, even buying up Hornby's Doublo, though they soon sold it. As of 2011, they were still producing model rail trains and accessories.
Bassett-Lowke
Bassett-Lowke began producing toy trains in the early 1900s. It's primary period of electric train vitality was between WWI and WWII and for a brief time in the 1950s. Bassett-Lowke tended to use other manufacturers like the German company Trix, for example, to make their products, and they functioned more as a distribution company. The company fell on hard times in the 1960s and was sold repeatedly over the next few decades. As of 1996, it's been operated by Corgi.
Exley
Edward Exley Ltd. produced a number of coaches and cars for Bassett-Lowke in the 1930s, until WWII. After the war, Exley produced made-to-order locomotives briefly, but discontinued this in the late 1950s. Exley manufactured coaches until 1962 when the factory burned down, with only minor distribution of outsourced products after that until 1995. In 1999, it was bought by Quintin Lucas. As of 2011, Exley was performing restoration work on their highly valued cars but not producing new products.