Do I need a swich fuse if the circuit is protected by a mcb

An MCB panelboard (as related to a panelboard)?

A Main Circuit Breaker panelboard will protect the "Load" or downstream (following circuits).

It does not protect in any way the incoming supply feeders. For example, if this is a Main Service Panelboard that has a MCB listed for 200 Amps, then the branch circuits sourced by the phase buss will be bars from that panelboard in the event of an overcurrent or fault condition.

However, opening the MCB at the panelboard, does not kill the supply side feeders into the panelboard. They remain Live and deadly.

If the panelboard is supplied by feeders from a meter, then the meter has to be pulled (removed) to kill the entire circuit.

Most AHJ now require a Main Service disconnect in front of the meter, primarily to protect fire personnel who may have to enter a burning building. The disconnect switch will shut all power off before it gets to the building.