WARNING: only fit fuses from established manufacturers
(avoid the pretty and cheap ones you can find on ebay)
If a blade fuse looks like a blade fuse and has a 10amp rating marked on, you assume it to be a 10amp blade fuse - WRONG
Out of interest (together with an element of suspicion), I tried to blow two unbranded 10amp fuses. They took 23amps continuous current - got hot (melted the plastic) but didn't blow. Same with a 7.5amp fuse - took 23amps without blowing. This means that, should something go faulty then at least 23amps could pass continuously into the fault. This would most likely result in smoke and a damaged wiring loom.
I checked the few original remaining fuses I had, marked Littelfuse - they all blew at rating plus about 20%, no more. Perfection.
SO there are good fuses and bad fuses. The eBay listings only seem to offer unbranded types - having been caught out once I won't be going down that route again. The original fuses for my Jaguar were made by Littelfuse - so after some hunting I ordered a set A04030 to be sure of having fuses that will actually BLOW when overloaded.