JavaMail API: SentDate problem

I have built an send email class around the JavaMail API v 1.1.3. Everything
works fine except that the message header sent date/time is 1 hour ahead of the
correct time.

Header date/time is set by:
msg.setSentDate((new GregorianCalendar()).getTime());
where msg is a Mime Message object.
At first, I assumed that the locale/time zone sys props were incorrectly set but
the following all display the correct time:
Calendar c = new GregorianCalendar();
System.out.println((c.getTime()).toGMTString());
System.out.println((c.getTime()).toLocaleString());
System.out.println((c.getTime()).toString());

Also, I would have expected the time to be either correct or one hour behind -
based on default props. As here in the UK we are in (a very wet) British Summer
Time, BST which is GMT + 1hour.

We are running JDK 1.2 on V4R5.

Thanks,

Keith