Split File into different sub file

[momoko]

Hi,
Currently I've one txt file that contains a few reports, I need to break them up but grouping the same report into one file. This is how the txt file look like : I want to have all with reportid 001 into one file and 002 into another. Please help.

ReportID:001
aaaaaaaaaaaaaaaaaaaa
bbbbbbbbbbbbbbbb
aaaaaaaaa

ReportID:001
ccccccccccccccc
cccddddddddddddd
ddddddddd

ReportID:002