for instance, using 5x20 1A Fast Ceramic Fuse 250V in an installation ...

In my view, the limited breaking capacity of these small fuses means that they should not be used directly from the incoming supply, nor from a large sub main with a similar load capacity and potential fault current to a DNO supply.

They may, in my view be used  to protect small loads that are connected to a sub-circuit.

To connect a clock, small extract fan, emergency light, or the like to a 6 amp circuit, or any size circuit up to say 32 amps.

But not suitable for use in a consumer unit, or other equipment connected directly to the incoming DNO supply.

Also suitable for use within equipment that is connected to the supply via a relatively small OCPD.

If a one amp fuse is required for direct connection to the DNO, or other similarly large supply, then in my view a physically larger fuse with a larger breaking capacity should be selected. Such as a BS 88 type.

In my view, the limited breaking capacity of these small fuses means that they should not be used directly from the incoming supply, nor from a large sub main with a similar load capacity and potential fault current to a DNO supply.

They may, in my view be used  to protect small loads that are connected to a sub-circuit.

To connect a clock, small extract fan, emergency light, or the like to a 6 amp circuit, or any size circuit up to say 32 amps.

But not suitable for use in a consumer unit, or other equipment connected directly to the incoming DNO supply.

Also suitable for use within equipment that is connected to the supply via a relatively small OCPD.

If a one amp fuse is required for direct connection to the DNO, or other similarly large supply, then in my view a physically larger fuse with a larger breaking capacity should be selected. Such as a BS 88 type.