Some small time ago, there was a shortage of trained drivers. Now the situation is reversed as EWS is making drivers redundant/early retirement.
You will have to undergo set of tests, which test your speed of reaction, mechanical puzzles and mechanical logic.
The speed of reaction test is the make or break of the whole test.
On 3/10/88 BR brought in the trainmans concept, where guards could go to be drivers after passing the above test.
Most of the drivers now, will be ex guards from that era, as BR stopped recruiting staff for any grade in the late 1990's.
At HM there was over 70 drivers, now this has shrunk to less than 30.