Where there is an island in the middle of a zebra crossing, wait on the island and follow Rule 19 before you cross the second half of the road - it is a separate crossing.

Rules for pedestrians · Crossings
Where there is an island in the middle of a zebra crossing, wait on the island and follow Rule 19 before you cross the second half of the road - it is a separate crossing.

In the Highway Code, MUST and MUST NOT identify legal requirements. Advice using should, should not, do or do not can still be used as evidence in court proceedings under the Traffic Acts to establish liability. The introduction explains this distinction.
The Code reads in order, and each of these names the rule it goes to rather than saying only ‘next’.
The rules the Code files beside this one, in its order.
The other groups in this part of the Code, and the rest of it.