Hi simon.
I had problem with this fuse box myself. It mainly powers electric seats/windows. the silver things you mention are overload breakers. say if your seat gets stuck an you keep your finger on the button these things will warm up and break the circuit untill they cool down again. the problem you have sounds very much like the one I had. it involves the wires that come though the bulkhead by your left leg. There's a very big red wire, it supplies the power to the ignition barrel, which then goes on to your fuse box that you mentioned, it could be the other way around though. first check that the connection by your left leg is ok on both sides of the connector as mine had broken off the tab that holds it in place and was only making intemitent contact, then drop the fuse box and check the fat wires on the back of that as they also break off the tabs, I can't remember the colours though. If the imobiliser is playing up it causes very similar symptoms, but it's best to check the simple stuff first.
Removing the imobiliser is not a quick job, set aside a day to do that. I found mine was a black cylinder about 6-7" long located under the dash with all black wires terminating into one end, it's full of relays set in resin so repair is out of the question, you will have to trace each wire to the connection made in the loom, cut it, then match the colour of the wires in the loom to put it back to original. on mine they cut out lengths upto 2ft long.
Hope that helps
Pete.
BTW. The wiring diags in the haynes comic arent worth a left handed w**K
