Simply awk/sed solution required - Split a file on fields

Hi All,

Trying to create a nice easy addition to a script using sed or awk to split a file with a given field.

---------------------------
INPUT FILE:


||AU|123456|E000|0212345678|email@domain.com|
TEXT
||US|123457|E567|0212344286||
TEXT
||AU|123456|E098|0212347129||
TEXT
||UK|123458|E123|0212347532|email@domain.com|
TEXT
---------------------------

This file needs to be split into multiple files. The two consecutive pipes ("||") will be considered to be the start of a new file. On line preceded by ||, the line contains multiple fields, the last of which is optional (email field).

Optimal solution will:

a) Use either sed, awk, a combination or ksh supported commands
b) Will be a short and as simple as possible
c) Will create files using the first and second fields as part of the filename and and increment (e.g. AU123456_001, US123457_002,AU123456_003,UK123458_004)

Thanks in advance,

Glenn