At time zone madness!

I've been trawling the net trying to find an answer to this, so sorry if
this is a common problem - I have tried looking before posting!

My problem is that when trying to SELECT a timestamp using "AT TIME ZONE
'Europe/London", it's subtracting an hour instead of adding it from a column
storing UTC dates.

The session time zone is set to UTC, and the field is a timestamp without
time zone.

However, if I do the same thing on now() instead of the result of my query,
it works!

More details below:

johngoss_cs=> set session time zone 'UTC';
SET

=> select now();
now
-------------------------------
2006-04-20 13:19:04.585175+00
(1 row)

=> select now() at time zone 'Europe/London';
timezone
----------------------------
2006-04-20 14:19:12.535543
(1 row)

At the time of running this the time was 14:10 in the UK (13:10 UTC)

=> select posttime from tbldiscussionreplies where rid = 300284;
posttime
----------------------------
2006-04-20 13:10:51.160939
(1 row)

Ok, so this is the raw posttime - which should always be UTC. Works fine.

=> select posttime at time zone 'UTC' from tbldiscussionreplies where rid =
300284;
timezone
-------------------------------
2006-04-20 13:10:51.160939+00
(1 row)

Try getting it at UTC - again fine - the session time zone is set to UTC, so
it doesn't change anything.

=> select posttime at time zone 'Europe/London' from tbldiscussionreplies
where rid = 300284;
timezone
-------------------------------
2006-04-20 12:10:51.160939+00
(1 row)

The problem!

For some reason this has subtracted an hour - making it two hours wrong!

The field is described as:
posttime | timestamp without time zone | not null default
timezone('utc'::text, now())

Any ideas?

Thanks!

John