Hi
I am a driving instructor who has passed many advanced driving tests and now teach instructors.
Block or 'selective' gear changing is not only allowed but is positively encouraged. In fact later this year or early next it will be marked against you if you DO NOT use the gearbox in an 'eco-safe friendly way'.
The method of 'sequencial' (1,2,3,4,5,4,3,2,1) is considered very old hat and was a method designed for cars like the old cortinas and morris minors where the brakes had no servo assistance and certainly none of the ABS, EBS, dual circiut and other braking systems that are around today.
Modern drivers would reduce the speed with the brakes and then select the most appropriate gear for the task in hand. As a guide it is gears to go and brakes to slow.
Nearly all learners today(strangely there is still the odd instructor who is stuck in thier ways but soon will HAVE to change) will wonder why Dad and Mum use so many fuel wasting stress causing and unnecessary gear changes and take to correct gear changing with absolute ease.
Further guidence can be found in the highway code(anyone read one lately) or Driving the Essential Skills published by the DSA who run the driving tests.