regex question (hopefully an easy solution?)

Hi Everyone...

This question is a follow up from my previous one (hopefully someone can 
help :) )

1) if I do
  deny message = Dangerous HTML tags in message ($regex_match_string)
    regex = <script>

In my exim config, then "<script>" in an email matches.... However this 
regex is weak against say <SCRIPT> or <ScRiPt> ... etc, etc

2) If I do
  deny message = Dangerous HTML tags in message ($regex_match_string)
    regex = [sS][cC][rR][Ii][pP][tT]

Then "<script>" also matches

3) However if I do
deny message = Dangerous HTML tags in message ($regex_match_string)
regex = <[sS][cC][rR][Ii][pP][tT]>

It never matches  "<script>"
I have tried escaping the< > characters like so
\<[sS][cC][rR][Ii][pP][tT]\>

But it also doesn't match :( - If I do this with grep and egrep it 
matches.  I have spent ages looking online with regex manuals trying to 
find if it is a special character, but no luck :( -

Can anyone give me some advice? I feel I am 99% of the way there.... 
just that last little 'push'.

Many Thanks,
Andrew.