The message
from John Rumm contains these words:

wrote:

The whole consumer unit is he

http://i250.photobucket.com/albums/g...e/100_1145.jpg

The strip that fails is he

http://i250.photobucket.com/albums/g...e/100_1146.jpg

The button that flips up is on the far left.

OK this makes it clearer. Looks like you have your "split load" consumer
unit built up from two different CUs.

I think that though it looks as if it makes use of some of the tooling
and components for separate CUs it's actually one phsyical plastic box.
We'd be a lot further on if the OP will just tell us what make it is.
My guess is it's Chinese and probably a Chint or clone of one.

With the lower one being RCD
protected and the top one just having a simple switch (which I presume
also cuts power to the whole lower CU as well).

Possibly -- but it might well be a simple split unit with the RCD for
the entire lower busbar fed from live side of switch disconnect.

There are a number of circuits on the CU that are known to be potential
causes of trouble: The hob, cooker, & immersion heater. Moving those to
the top CU might be better (you would need to combine a couple of
circuits on the top one to make space since you only have one free way
up there).

Agreed as to the most probable sources of trouble, especially with a
30mA RCD. However there are two spare ways in the bottom so there's
room to put in a second switch-disconnect and split the busbar in the
bottom row, always assuming that parts to fit are available.

If only the OP would come back with a bit more info.