Pilot's Notes General AP2095
4. Manœvres not Permitted
(i)
Intentional spinning of operational aircraft
(iv)The reasons underlying these prohibitions are partly considerations of strength, partly of control. Aircraft are designed to fulfil their operational role and not to perform manœvres of no operational value.
That 609 Sqn pilot...naughty! Tsssk tssk!
However pilots were trained to spin in order to learn how to stay calm and recover the aircraft - during WW1 pilots who got into a spin often didn't know how to recover; until a training regime was put in place spinning into the ground was a common cause of death.